Novel kinase-start gene conferring resistance to plant disease and transgenic plants comprising it

ABSTRACT

An isolated nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain is provided, as well as plant cells and transgenic plants comprising said nucleic acid molecule, said transgenic plants being resistant to plant disease.

GOVERNMENT RIGHTS

This invention was made in part with the United States Government support under grants USDA/NRI20053530115906 and USDA/NRI20065560616629 awarded by the US Department of Agriculture, and with the support of the United States Israel Binational Agricultural Research and Development Fund (BARD) under grant US402407. The U.S. Government has certain rights in this invention.

TECHNICAL FIELD

The present invention relates to a novel kinase-START gene conferring resistance to plant disease, and transgenic plants comprising it for use in methods to control plant disease, such as stripe rust in cereal crop plants.

BACKGROUND ART

Bread wheat (Triticum aestivum L.) provides approximately 20% of the calories consumed by humankind. The increasing world demand for cereals requires improved strategies to reduce yield losses due to pathogens. Wheat stripe rust, caused by the fungus Puccinia striiformis f. sp. tritici (PST, Table 1) affects millions of hectares of wheat and virulent races that appeared within the last decade are causing large yield losses (Singh et al., 2004). Historically, resistant varieties have provided an economical and “environmentally friendly” method to control stripe rust. Numerous race-specific resistance genes have been deployed by breeders, but each had limited durability presumably because of rapid pathogen evolution. In contrast, broad-race resistance genes (i.e. “slow-rusting”) have a broader spectrum of resistance and are generally more effective at adult plant stages, provide partial resistance, and usually confer more durable resistance than race-specific genes (Singh et al., 2004). Unfortunately, our understanding of broad-race resistance is limited because none of these genes has yet been cloned.

SUMMARY OF INVENTION

The gene Yr36, which confers non race-specific resistance to stripe rust at relatively high temperatures (above about 15° C.), has been cloned and sequenced in accordance with the present invention. The cloned gene, referred to herein as WKS1, is shown herein to be equivalent to Yr36.

The present invention is directed, in one aspect, to an isolated nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain. In some embodiments, the isolated nucleic acid molecule encodes a WSK1 polypeptide.

In some aspects, the present invention relates to an isolated nucleic acid molecule that is a complementary to the above isolated nucleic acid molecule comprising a START domain and/or a kinase domain.

In further aspects, the present invention relates to an isolated nucleic acid molecule comprising a nucleotide sequence having promoter function or a variant or a fragment thereof, wherein said promoter is a temperature-sensitive promoter. This temperature-sensitive promoter nucleotide sequence may be operably linked to the above isolated nucleic acid molecule comprising a START domain and a kinase domain.

In further aspects, the present invention provides a vector comprising the isolated nucleic acid molecule comprising a START domain and a kinase domain of the invention that may be operably linked to the above isolated nucleic acid molecule comprising a nucleotide sequence having promoter function.

In additional aspects, the present invention provides a host cell, in particular a plant cell, and a transformed seed, that contain the vector or the isolated nucleic acid molecule comprising a START domain and a kinase domain of the present invention.

In additional aspects, the present invention provides a transgenic plant comprising the host cell, wherein the polypeptide encoded by the nucleic acid molecule confers to the transgenic plant resistance to diseases caused by specific pathogen races or they may confer non-race specific broad-spectrum resistance.

In additional aspects, the present invention is directed to a method for conferring resistance to stripe rust in a cereal crop plant, said method comprising transforming said plant with a vector or a nucleic acid molecule as defined herein above. In some embodiments, the cereal crop plant is wheat.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the effect of plant age on Yr36 resistance response (10/25° C.). UC1041 near isogenic plants with and without Yr36 at different developmental stages were inoculated on the same day with race PST-113 and the percent leaf area covered with pustules was evaluated three weeks later using the pd program (FIG. 3). (panels A and E) Inoculated at 1st leaf and scored at 3rd-4th leaf. (panels B and F) Inoculated at 4th leaf and scored at 6-7th leaf (panels C and G) Inoculated at elongation stage and scored at flag leaf emergence. (panels D and H) Inoculated at heading and scored at anthesis. Plants at the first two developmental stages are classified as juvenile plants, whereas those at the two later stages are classified as adult plants. The black areas in panel C are teliospores. Values are averages of four plants±SEM of the percentage area covered with PST pustules. Bar=2 mm.

FIG. 2 Map-based cloning of Yr36. (panel A and panel B) Phenotype of susceptible parent Langdon with PST sporulation (A) and partially resistant parent RSL65 (B). Bar=1 mm. (panel C and panel D) Genetic maps of colinear regions of rice chromosome 2 (C) and wheat chromosome 6B (D). (panel E) Physical map of the Yr36 region. Genes are represented by colored arrows and the deleted region in Langdon by a light blue line. The left-pointing black arrow points in the direction of the telomere. The yellow rectangle delineates the Yr36 region (panel F) Structure of the WKS genes. Exons are represented by rectangles and the kinase and START domains are shown in blue and red, respectively. The green hatched box represents the LINE retrotransposon.

FIG. 3 shows examples of leaves used for quantification of the percentage of leaf area covered with PST pustules. (panel A and panel E) Scanned images of 5-cm segments of wheat leaves. (panel C and panel G) Each pixel in (A) and (E) was categorized by the pd program as either leaf (green), Puccinia striiformis f. sp. tritici (PST) (red) or background (black). Images in the right column are an enlargement of the image in the rectangle in the left column. (A to D) Susceptible RSL 11-19 with pustules covering 6.9% of the surface area in the segment shown in (A). (E to H) Resistant RSL3-28 with pustules only on 0.9% of the segment shown in (E). Contrast and brightness were manipulated in (B) and (F) to better show pustules. The white areas in (E) are necrotic patches. Bar=5 mm. The pd program is freely available at http://plantpathology.ucdavis.edu/faculty/epstein/.

FIGS. 4A-C show the reaction to Puccinia striiformis f. sp. tritici (PST) in parental and 13 critical recombinant substitution lines (RSLs) used to map Yr36. (A) Left panel, susceptible parent LDN; Right panel, resistant parent RSL65. Plants at the 3-leaf stage were inoculated with PST-100 and then incubated in a growth chamber with a daily 10/25° C. cycle. (B) Leaves of susceptible recombinant progeny have prodigious sporulation in the orange pustules. (C) Leaves of resistant recombinant proginy have necrotic regions with reduced sporulation. Images of the progeny leaves are perpendicular to the parental leaves. Bars=1 mm.

FIG. 5 depicts the physical contig of the Yr36 region. The top line summarizes the information from the HindIII fingerprinting of the B genome BACs listed below and the sequencing of BACS 391M13 and 1144M20 (in blue). Colored ovals represent markers used for the fine mapping of Yr36, whereas colored arrows represent genes WKS1, WKS2, IBR1, and IBR2 linked to Yr36. Markers Xucw129 and Xucw148 flank the Yr36 region (186-kb, yellow shaded square). Markers Xucw125, Xucw126, and Xucw130 and genes WKS1, WKS2, and IBR1 were not amplified in Langdon, suggesting the presence of a large deletion (between 149 and 183-kb long based on current markers). The left-pointing black arrow at the top line points in the direction of the telomere. The bar above the top line delineates the LDN deleted region.

FIG. 6 depicts the sequence annotation of the Yr36 region. (Panel A) Graphic representation of the annotation of the 314-kb sequenced contig. Two large direct duplications were identified: 1a/1b and 2a/2b. The 1a and 1b duplicated regions each include a putative gene which encodes for a protein with an ‘in between RING finger’ domain (IBR), designated as IBR1 and IBR2. The 2a and 2b regions include genes WKS1 and WKS2, respectively. The X8 putative gene (=Xucw127) is outside the Yr36 critical region defined by markers Xucw129 and Xucw148. Boxes outside the duplicated regions represent transposable elements. Half-arrows indicate putative genes. The 262-bp overlap between the 2b and 1b duplication is indicated by a bright blue box. (Panel B) Detail of the duplicated regions. The 1a (64.5-kb) and 1b (32.3-kb) regions are 96% identical across 31.3-kb. The 1a region has four unique retrotransposon insertions and a series of repeats absent in the 1b segment. The 2a (19.0-kb) and 2b (94.9-kb) regions are 81% identical across 7.9-kb of shared sequence, suggesting that this duplication is older than the 1a/1b duplication. The 2b region is larger than the 2a region because of a 70.2-kb insertion of multiple nested retrotransposons (shown in different scale). Conserved sequences between the corresponding duplicated regions are represented by similar colors. GenBank accession EU835198 includes a detailed annotation of the region.

FIG. 7 shows selected mutations in the WKS1 kinase domain. CLUSTALW alignment of the kinase domains (smart00219) from the three closest rice and Arabidopsis homologues to WKS1 and WKS2. Amino acid residues that form the ATP (▴) and substrate (*)-binding pocket are labeled. Residues that form part of the catalytic (CL) or activation (AL) loop are underlined. The red diamond indicates the site of the conserved arginine (R) residue within the catalytic loop that is used to classify kinases as either RD on non-RD. WKS1 has a glycine (G) residue at this position, and is therefore a non-RD kinase. Amino acids affected by the mutations resulting in WKS1 loss of function are indicated by bold orange letters. The Targeting Induced Local Lesions in Genomes (TILLING) mutant line designation and the amino acid change in that line is indicated above the WKS1 sequence.

FIGS. 8A-B depict the aligned WKS1 START domain in several plant species. (A) CLUSTALW alignment of the START-domain region surrounding the D477N mutation in T6-567 (bold orange letter). The aspartic acid residue (D) is conserved across all plant species examined as well as across the closest human START genes (StarD6, D14, D15; not shown). The alignment includes the closest plant homologues from Arabidopsis (At), rice (Os), Poa, Populus, Vitis, Sorghum (Sb), Zea, and moss Physcomitrella patens (Pp). Complete sequences are available in Genbank or Phytozome (http://www.phytozome.net/). (B) Partial alignment of the START domain C-terminus region. The orange arrow indicates the last common amino acid residue between WKS1 transcript variants WKS1.1 and WKS1.2.

FIG. 9 shows micrographs of 6 mutants with changes in conserved amino acids in WKS1 for the functional validation of Yr36 by mutational analysis. (panels A to F) Leaf surfaces 11 days after PST inoculation. Bar=5 mm. Numbers below leaves are average percent leaf area with pustules±SEM (N=8, FIG. 12). An ANOVA of the log-transformed data showed significant differences (P<0.01) between mutant and control lines. (A) The common wheat breeding line UC1041 without Yr36. (B) UC1041+Yr36 isogenic line used for mutagenesis. (C and E) Lines T6138 and T6-312 with homozygous mutations in the WKS1 kinase domain. (D and F) Sister lines without the mutations (see Example 2). (G and H) A dual-channel, confocal microscopic z-series inside a wheat leaf 13 days after PST inoculation. Bar=20 μm. The uvitex-stained fungus (false-color blue) and autofluorescing wheat leaf cells (false color red) are visible. (G) The susceptible T6-312 mutant has an extensive mycelial network in which each (invisible) plant mesophyll cell (selected cells shown as M) is encircled by a hypha. (H) The T6-312 control line has a poorly developed fungal network surrounded by autofluorescent mesophyll cells that presumably were involved in the resistance response. (I and J) Separate channels of panel (H).

FIGS. 10A-B show the effect of WKS1 and WKS2 mutations on PST resistance (Mutant experiment 1). Three WKS2 (A) and 5 WKS1 mutants (B) (see Example 2) were inoculated at the 4th-leaf (juvenile) stage with race PST-113. The susceptible wheat line UC1041 (without Yr36) and the isogenic line UC1041+Yr36 were used as controls (FIG. 10A, panels B and A, respectively). Further in FIG. 10A: WKS2 mutants T6-826 (panel D); T6-480-2 (panel E); T6-960 (panel F). In FIG. 10B: WKS1 mutants T6-312 (panel B); T6-138 (panel C) T6-569 (panel D); T6-480-1 (panel E); and T6-86 (panel F). Sister lines of mutants T6-826 FIG. 10A, panel C) and T6-312 (FIG. 10B, panel A) homozygous for the absence of the mutation also were included as controls. The margins of the leaf regions with pustules were marked with a black marker 15 days after inoculation and pictures were recorded five days later.

FIG. 11 shows loss of PST resistance in WKS1 START mutant T6-567 (Mutant experiment 3). The T6-567 line (discovered after Mutant experiments 1 and 2) has a mutation in a conserved codon in the START domain (FIG. 8A). PST infection in this mutant line (panel D) was compared with a sister line homozygous for the absence of this mutation (panel C). Susceptible UC1041 (panel B) and resistant UC1041+Yr36 (panel A) also were tested as controls. Plants were inoculated with race PST-113 at the stem elongation (adult plant) stage.

FIG. 12 depicts WKS1 transcript levels (upper panel) and resistance phenotype in transgenic wheat plants (lower panel). The transcript levels were analyzed using the 2^(−ΔΔCT) method (see Example 2 and Materials & Methods). Average WKS1 transcript levels (±SEM) in independent transgenic events 17a (T17a; 5 plants) and 26b (T26b; 7 plants) were determined by quantitative RT-PCR. Negative controls are the un-transformed variety Bobwhite (Bw) and the average of three T1 sister lines of 17a without the transgene (C17a). Leaf phenotypes: S=susceptible, R=resistant. Bar=2 mm. Southern blots and transcription profiles of individual T1 plants are shown in FIG. 13.

FIG. 13 depicts the characterization of T1 plants from independent transgenic events 17a (T17a) and 26b (T26b) in hexaploid wheat variety Bobwhite (Bw). (panel A) Resistance (R) or susceptible (S) response on leaves after inoculation with race PST-113. (panel B) WKS1 transcript levels, analyzed using the 2^(−ΔΔCT) method, before infection as determined by Q-PCR. Values are averages of 6 leaves±SE of the means. The red dotted line indicates WKS1 transcript level in a non-transgenic UC1041+Yr36 positive control. (panel C) Southern blots hybridized with WKS1 showed absence of the transgene in 17a-1, 17a-3 and 17a-18 (in red) and presence in the other five 17a lines. The blue arrow indicates the expected size of the restriction fragment that hybridizes with the WKS1 probe.

The 17a lines without the transgene were as susceptible as the negative Bobwhite control. Transgenic lines with WKS1 transcript levels similar or higher than the positive control UC1041+Yr36 (dotted red line) were resistant to PST-113 and showed little or no sporulation. Line 26-8, which had an intermediate resistance reaction (R/S), had the lowest WKS1 transcript levels of the transgenic lines. Since the endogenous WKS1 in UC1041+Yr36 is in a different genetic background, its transcript levels should be considered just as an approximate positive control.

FIG. 14 is a graphical representation of WKS1 alternative transcript variants. Cloning and sequencing of 56 WKS1 cDNA clones revealed six transcript variants designated WKS1.1 to WKS1.6. Primers WKS1_F5/R5 and WKS1_F4/R4 were used to amplify transcript variant WKS1.1 and WKS1.2-6, respectively. Primer WKS1_R5 anneals to the WKS1.1 exon 10-11 splice junction whereas primer WKS1_R4 anneals to the WKS1.2-6 sequence of exon 10 that is missing from WKS1.1. The kinase and START domains are shown in blue and red, respectively. Stop codon is marked by *. Bar=500 bp.

FIG. 15 shows the effect of temperature (T) and PST inoculation (I) on transcript levels of WKS1 transcript variants WKS1.1 and WKS1.2-6 in RSL65. Quantitative RT-PCR transcripts of WKS1.1 are indicated in black and those of WKS1.2-6 in gray. PST-inoculated plants (I+) are indicated by stripes and non-inoculated controls (I−) by solid colors. Leaf-samples from RSL65 plants were collected 3, 9 and 16 days post inoculation (DPI) with race PST-100. Half of the plants were not inoculated. Each datapoint is the average of 6 samples±SE of the mean. The transcript levels were analyzed using the 2^(−ΔΔCT) method (see Example 2 and Materials & Methods). No significant interactions between temperature and inoculation were detected in the individual 2-way ANOVAs except for panel A (significant differences between inoculation classes only at low temperature). *: P<0.05, **: P<0.01, ***: P<0.001, and NS: not significant. Each data point is an average based on six replicates (±SEM).

FIG. 16 shows the effect of temperature and infection with PST on WKS1 transcript variants. The effect of high (10/35° C.) and low (10/15° C.) temperatures on transcript levels of WKS1.1 (black bars) and WKS1.2-6 (gray bars) was determined by Q-PCR. The transcript levels were analyzed using the 2^(−ΔΔCT) method (see Example 2 and Materials & Methods). Leaf-samples from RSL65 plants were collected 3, 9 and 16 days post inoculation (DPI) with race PST-100. Half of the plants were not inoculated. Each datapoint is the average of 6 samples±SE of the mean. Since the ANOVAs showed significant interactions between transcript variants and temperatures, simple effects for transcript variants within each temperature are presented above each pair of bars. (panels A to C) Inoculated. (panels D to F) Non-inoculated. **: P<0.01, ***: P<0.001, and NS: not significant.

FIG. 17 shows in-gel kinase activity of GST-WKS1_Kinase. (panel A) Coomassie Blue stained gel of purified proteins from GST-WKS1_Kinase fusion protein (KIN, red arrow) and the GST control vector (GST). (panel B) In-gel kinase activity assay using casein (1 mg/mL) as a phosphorylation substrate. Radioactive bands were visualized using a Storm 860 PhosphorImager. The in-gel kinase assay was repeated twice with independently expressed fusion proteins with identical result. (panel C) Western blot using a GST-antibody.

FIG. 18 shows PCR markers used to determine WKS1 and WKS2 distribution among different Triticeae species. “+” indicates presence, and “−” indicates absence, of WKS1 or WKS2 in the Triticeae species indiciated at the top of each lane: A, UC1041+Yr36; B, Kronos (durum); C, Ae. comosa; D, L. elongatum. ID, Inter domain; rpt, repetitive.

DETAILED DESCRIPTION OF THE INVENTION

The novel nucleic acid sequence of WKS1 of the invention encodes for a polypeptide comprising both a steroidogenic acute regulatory protein related lipid transfer (START) domain and a kinase domain. The START domain is a protein domain spanning ˜210 residues, which is conserved in plants and animals, serves as a binding interface for lipids and has been implicated in many distinct processes. The crystal structures of three human proteins comprising START domains have been solved, revealing a conserved ‘helixgrip’ fold that forms an inner tunnel wide enough to accommodate the hydrophobic lipid. As is shown in the Examples hereinafter, the amino acid sequence of the START region of WKS1 is of SEQ ID NO: 1.

It has further been found in accordance with the present invention that the WKS1 kinase has high similarity to several Arabidopsis WAK-like kinases, but WKS1 lacks the additional domains characteristic of WAK-like kinases. The WKS1 kinase, which has a Ser/Thr kinase domain, belongs to the non-RD kinases, which are frequently involved in the early steps of the innate immune response. The kinase domain of WKS1 has the amino acid sequence as set forth in SEQ ID NO: 2.

The term “Ser/Thr kinase” is used herein to indicate a kinase that is capable of phosphorylating the OH group of serine or threonine. The term “non-RD kinase domain” is used herein to indicate that the protein lacks the conserved arginine (R) residue within the catalytic loop that is used to classify kinases as either RD or non-RD kinases.

The combination of the kinase and START domains in WKS1 apparently is the result of a novel domain shuffling because, before the present invention, these two domains have not been found together in any other organism. For example, we searched the rice and Arabidopsis genomes for genes encoding for both kinase and START domains to look for a possible orthologue of WKS1. We did not find this combination in rice but in Arabidopsis we found putative gene MGH6.22 (AB026645) that encodes for a 1,088 amino acid protein (BAB01397). BAB01397 has a START domain in the N-terminal region followed by multiple leucine-rich repeats (LRRs), and a protein kinase catalytic domain in the C-terminal region. There is no full-length cDNA to support this annotation, and the protein record Q9LK66 has been discontinued and replaced by two adjacent but separate genes: At3g13062 (NP_(—)850573, an unknown protein with similarity to a START domain) and SRF4 (STRUBBELIG-RECEPTOR FAMILY 4, serine/threonine kinase) supported by multiple ESTs.

Using primers from At3g13062 and SRF4, we cloned two full-length cDNAs from Arabidopsis (Columbia ecotype) that include both At3g13062 and SRF4 coding sequences. However, both cDNAs have premature stop codons between the START and the LRR repeats, one of which is similar to the stop codon in At3g13062 (GenBank FJ154117 and FJ154118).

The kinase and START domains of WKS1 are in a different order than in the At3g13062-SRF4 cDNA. In addition, the two WKS1 domains are more similar to other Arabidopsis proteins than to At3g13062-SRF4 (BLASTP searches of Arabidopsis RefSeq protein database). The START domain and the adjacent 5′ inter-domain region of WKS1 are more similar to Arabidopsis EDR2 (NP_(—)193639, 56% identity over 337 amino acids, E=3e⁻¹⁰³) than to At3g13062 (NP_(—)850573, no BLASTP significant similarity). Similarly, the WKS1 kinase domain is more similar to the WALL ASSOCIATED KINASE 4 (NP_(—)173544, 40% identity over 314 amino acids, E=1e⁻⁵¹) than to SRF4 (30% identity over 280 amino acids, E=1e²⁸). These results indicate that the domains encoded by At3g13062 and SRF4 are not likely orthologous to the kinase and START domains in WKS1.

A BLASTP search in rice showed that the closest protein to the WKS1 kinase domain is EAY97604 (60% identical over 323 amino acids E=9e⁻¹⁰⁵) and that the closest one to the START domain is ABB47745 (66% identical over 335 amino acids, E=2e⁻¹²³) which is 72% identical to Arabidopsis EDR2 over its entire length (E=0). These two genes (or closely related ones) are the most likely source of the shuffled domains that originated WKS1. The WKS1 kinase is classified as a non −RD kinase because it lacks the arginine (R) residue preceding the invariant aspartate (D) in the activation domain.

START domains are lipid/sterol binding modules that are conserved from animals to plants (Schrick et al., 2004). Although the specific ligands for some human START domain proteins are known (e.g. StAR protein binds cholesterol and CERT protein binds ceramides), a function in ligand binding has not been verified for any START plant protein so far. However, Arabidopsis plants with mutations in sterol biosynthesis genes share common phenotypes with mutants for homeodomain-START genes, which suggests that these proteins may be controlled by binding sterols. In addition, protein modeling of plant START domains based on the crystal structure of human START proteins implicates similar molecular ligands, and suggests that these proteins have retained common functions in evolution (Schrick et al., 2004). EDR2, a START domain protein involved in the Arabidopsis response to powdery mildew, localizes to the endoplasmatic reticulum, plasma membrane and endosomes, which is also consistent with a role of the START domain in lipid sensing and trafficking.

Amongst the 35 Arabidopsis proteins with START domains, the EDR2START domain is the closest to the WKS1 START domain. However, EDR2 and WKS1 differ in other conserved domains present in these proteins. WKS1 has an additional kinase domain, whereas EDR2 has additional PH (plekstrin homology) and DUF1336 (unknown function) domains. This may explain why WKS1 confers resistance, whereas EDR2 is a negative regulator of pathogen-induced disease resistance. In spite of these differences, the two genes share a late-acting resistance phenotype associated with necrotic lesions and programmed cell death. As shown in Example 2, wheat plants with a mutation in the WKS1 START domain are susceptible to PST and lack the necrotic lesions characteristic of plants with wild WKS1 alleles, which indicates that this domain is necessary to trigger the hypersensitive response.

The edr2 phenotype is very similar to the phenotype of both edr1 and edr1-edr2 double mutants suggesting that these two genes are part of the same signal transduction pathway. EDR1 encodes a CTR-1 Ser/Thr kinase suggesting that EDR2 might be a phosphorylation target of EDR1. Phosphorylation has been also shown to be important for START domain function for at least one animal protein and to modulate the role of ceramides in programmed cell death in Arabidopsis. The presence of an active kinase and a putative START domain within a single protein (WKS1) provides a new tool to study interactions between kinases and START domains, but more importantly, as is shown herein below in Example 2, both the kinase and START domains are necessary for the resistance response.

In view of the above, in one aspect, the present invention relates to an isolated nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a START domain and a kinase domain. In certain embodiments, the START domain consists of SEQ ID NO: 1, or a variant or a fragment thereof, and the kinase domain is a non-RD kinase domain, such as a Ser/Thr kinase domain, for example of SEQ ID NO: 2, or a variant or a fragment thereof.

As is shown herein in the examples, the cloning and sequencing of 56 full-length WKS1 cDNAs revealed six alternative transcript variants (WKS1.1-6, Example 4). WKS1.1 encodes a complete WKS1 protein (SEQ ID NO: 3), whereas the other five (WKS1.2-6) lack exon 11 and encode proteins with truncated START domains (SEQ ID NOs: 4-7, respectively). Some of the missing amino acids are well conserved across the plant kingdom. Of course, any nucleotide sequence encoding the polypeptides of SEQ ID NOs: 3-7 could be used according to the present invention, preferably the nucleic acid sequence of the transcripts variants as set forth in SEQ ID NOs: 9-14 encoding for the proteins of SEQ ID NOs: 3-7, respectively, and most preferably the nucleic acid sequence of the transcript variant WKS1.1 of SEQ ID NO: 9.

Thus, in certain embodiments, the isolated nucleic acid molecule of the invention comprises a nucleotide sequence that encodes a polypeptide selected from the polypeptides herein designated WKS1.1 (SEQ ID NO: 3), WKS1.2 (SEQ ID NO: 4), WKS1.3 (SEQ ID NO: 5), WKS1.4 (SEQ ID NO: 6), WKS1.5 (SEQ ID NO: 7) and WKS1.6 (SEQ ID NO: 8), or a variant or a fragment of said polypeptide. In certain embodiments, the isolated nucleic acid molecule comprises any one of the nucleotide sequences of SEQ ID NOs: 9-14. In one embodiment, the isolated nucleic acid molecule comprises the nucleotide sequences of SEQ ID NOs: 9.

The variants of the present invention are nucleic acid molecules of a sequence having at least about 60% identity, for example, at least 85% sequence identity, at least 90% sequence identity, at least 95% sequence identity, or at least 99% sequence identity with a nucleic acid sequence identified above as well as nucleic acid molecules encoding the polypeptides of the invention but comprising degenerate codons. The sequence identity is based on known alignment methods, for example, the ClustalW alignment method. On the protein level, the polypeptide variants encoded by the nucleic acid molecules of the present invention have at least 60% identity, for example at least 70% sequence identity, at least 80% sequence identity, at least 85% sequence identity, at least 86% sequence identity, at least 90% sequence identity, at least 95% sequence identity, or at least 99% sequence identity with an amino acid sequence identified above. The variant may also be a splice variant of the polypeptide. Both the variants and fragments of the nucleic acid molecules and of the polypeptides encoded thereby are encompassed by the present invention as long as they exhibit the same biological activity as said polypeptides, i.e. that they have kinase activity and START domain activity such as the binding of sterols, and/or confer resistance to stripe rust in a cereal crop plant.

An accepted method of controlling plant diseases is the development of disease resistant plants expressing resistance genes. These genes may afford resistance to specific pathogen races or they may confer non-race specific resistance, or broad-spectrum resistance. Often, broad-spectrum resistance genes confer resistance to a variety of plant diseases caused by pathogens as different as viruses, fungi and bacteria.

A resistant plant is characterized by the appearance of necrotic patches in the leaves in response to the pathogen, whereas such patches do not appear in susceptible plants following infection. Furthermore, the terms “resistant and resistance” are used herein to describe the ability of the plant to withstand damage to plant tissue caused by a pathogen. For example, a variety or line resistant to a certain pathogen produce significantly higher yield than a susceptible variety in the presence of the pathogen. Plants can also be classified according their response to fungi into three infection types (IT) (R. F. Line, A. Qayoum, Technical Bulletin 1788, United State Department of Agriculture, 1992): 0-3 (resistant, none to trace level sporulation), 4-6 (intermediate, light to moderate sporulation), 7-9 (susceptible, abundant sporulation). In accordance with the findings of the present invention, susceptible lines exhibit IT values ranging between about 6 to about 7 and resistant lines exhibit IT values ranging between about 2 to about 3. Lines can also be classified according to relative leaf area covered with fungi pustules. Accordingly, lines that are not significantly different from the susceptible line LDN and significantly more susceptible than the resistant line RSL65 are classified as susceptible (“S”), whereas lines that are not significantly different from RSL65 but significantly more resistant than LDN are classified as resistant (“R”). Naturally, the reference susceptible and resistant lines may be chosen from any relevant susceptible or resistant lines, depending on the plant species, variety or line studied. As shown herein below, susceptible lines exhibit a percentage area covered with pustules ranging between about 6 and about 13, while resistant lines exhibit a percentage area covered with pustules ranging between about zero and about 3.

Thus, a plant to which broad-spectrum resistance to a certain pathogen has been conferred is a plant in which necrotic patches appear in the leaves in response to the pathogen. Furthermore, a plant which has acquired broad-spectrum resistance produces significantly higher yield than a susceptible variety in the presence of the pathogen; it can be characterized as a plant of infection type 4-6, preferably 2-4, and most preferably O-3, or as a plant that has a relative leaf area covered with fungi pustules that is significantly lower than that of the susceptible line LDN (or a different susceptible line) and not significantly different from that of the resistant line RSL65 (or a different resistant line), preferably having a relative leaf area covered with fungi pustules ranging between about zero and about 3.

The term “significant” as used herein refers to its statistical meaning; i.e. when using a commonly known statistical test to analyze differences among two or more independent groups, such as a Student's t-test or ANOVA, and the calculated p-value is lower than α=0.05, then the groups are significantly different.

The term “about” as used herein refers to the adjacent stated value plus or minus 10% or lower, such as 8%, 5% or 2%.

Thus, in one embodiment, the polypeptide encoded by the nucleic acid of the present invention, or a variant or a fragment thereof, confers to a plant broad-spectrum resistance to a plant disease, in particular a fungal plant disease. The plant protected by this polypeptide may be a cereal crop plant, such as, but not limited to wheat or barley. The wheat species contemplated by the present invention are, for example, but not limited to, common wheat or bread wheat (T. aestivum), durum (T. durum), einkorn (T. monococcum), and spelt (T. spelta). The barley cultivars contemplated by the present invention are for example, but not limited to, two-row barley (Hordeum distichum, Hordeum vulgare), and six-row barley (Hordeum vulgare).

The fungal plant disease may be caused by a Erysiphales or a Puccinia fungus. For example, the disease may be powdery mildew caused by a Erysiphales fungi, stem rust, also known as black rust or cereal rust caused by Puccinia graminis, brown rust of wheat caused by Puccinia recondite or wheat rust caused by Puccinia triticina.

In certain embodiments, the plant is cereal crop plant, such as wheat or barley and the fungal plant disease is a rust disease caused by a Puccinia fungus, such as Puccinia striiformis, in particular wheat stripe rust caused by Puccinia striiformis f. sp. tritici.

In another aspect, the present invention relates to at least one isolated nucleic acid molecule that is a complement of, i.e. is complementary to, a nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising SEQ ID NO: 1 and/or SEQ ID NO: 2. This at least one nucleic acid molecule may be used to identify cells comprising nucleic acid sequences encoding for WKS1 polypeptides, variants or fragments thereof. The complement nucleic acid molecule may have a sequence of at least about 60% identity, for example, at least 85% sequence identity, at least 90% sequence identity, at least 95% sequence identity, or at least 99% sequence identity with the exact complement of SEQ ID NO: 1 and/or SEQ ID NO: 2.

It has further been found in accordance with the present invention that the nucleic acid sequence present upstream of the ATG start codon of the nucleic acid encoding the WKS1 protein of the present invention, comprises a temperature sensitive promoter which is up to about 3000 basepairs, or between about 1000 and about 2566 basepairs in length. This promoter may be utilized for driving the expression of genes conferring important traits to a plant in a temperature dependent manner, thus inducing the expression of such genes only at certain temperature, for example, above about 15° C.

Thus, in a further aspect, the present invention relates to an isolated nucleic acid molecule comprising a nucleotide sequence present upstream of the ATG having a size selected from about 3000 basepairs and between about 1000 and about 2566 basepairs, for example of SEQ ID NO: 15, having promoter function, or a variant or a fragment thereof, wherein the variant and the fragment maintain the promoter function of the intact promoter. In one embodiment, the nucleic acid molecule is operably linked to a heterologous transcribable polynucleotide molecule, such as, but not limited to a nucleic acid molecule of the present invention that is encoding a WKS1 polypeptide, variant or fragment thereof.

In another embodiment, the nucleic acid molecule having promoter function is induced at a temperature selected from at or above about 15° C., between about 15° C. and about 35° C., between about 20° C. and about 35° C., and between about 20° C. and about 25° C. or between about 25° C. and about 35° C.

The present invention further provides a vector comprising a nucleic acid molecule according to the present invention, and optionally a nucleotide sequence encoding a heterologous protein, wherein said nucleic acid molecule is operably linked to a promoter that drives expression of the coding sequence of said nucleic acid molecule in a plant cell. The heterologous protein maybe a marker for following protein expression or for facilitating purification, such as Green Fluorescent Protein, a His-tag (e.g. His₆), a (His-Asn)₆ tag, a Flag tag, or preferably glutathione S-transferase (GST).

The promoter driving the expression of the nucleic acid molecule may be a constitutive promoter such as a ubiquitin promoter, a pathogen-induced promoter such as a Puccinia-induced promoter or a temperature-sensitive promoter, such as the temperature sensitive promoter comprised by the nucleic acid sequence present upstream of the ATG start codon of the nucleic acid encoding the WKS1 protein of the present invention, as defined herein above.

The present invention further relates to a host cell that contains the vector or a nucleic acid molecule of the present invention, to a transgenic plant comprising a plant host cell that contains the vector or nucleic acid molecule of the present invention, and to a transformed seed comprising the vector or nucleic acid molecule according to the present invention. The host cell may be a bacterial, yeast or insect cell. In one embodiment, the cell is a plant cell.

The present invention further contemplates methods of transforming/transfecting plants with the nucleic acid molecule of the present invention, in order to confer to said plants resistance to a plant disease

In certain embodiments, the nucleic acid molecule is inserted into a vector, e.g. a plasmid, comprising nucleotide sequences providing for the correct incorporation of the nucleic acid molecule into the genomic DNA of a host cell and/or for expression of the polypeptide encoded by the nucleic acid molecule. The vector may be circular or it may be a linear nucleic acid molecule.

Non-limiting examples of techniques for transformation of plant cells with foreign nucleic acids are: (i) Agrobacterium-mediated transformation, in which the foreign nucleic acid is introduced into the plant cell by first transfecting the Agrobacterium with a vector comprising the foreign nucleic acid and then bringing the Agrobacterium into contact with the plant or plant tissue to be transformed. The Agrobacterium then inserts the vector into the cell. Unfortunately, many plants are not transformable by this method; (ii) the nucleic acid molecules are inserted directly into the plant cells by known techniques, for example: (a) Bombardment, in which small gold or tungsten particles are coated with plasmids or nucleic acid fragments and propelled through the cell walls of young plant cells or plant embryos. Some genetic material will stay in the cells and transform them. The transformation efficiency can be lower than in Agrobacterium-mediated transformation, but most plants can be transformed with this method; (b) Electroporation, which makes transient holes in cell membranes using electric shock allowing the nucleic acid molecules to enter the cell; or (iii) viral transformation in which the desired genetic material is packaged into a suitable plant virus and the modified virus is allowed to infect the plant. If the genetic material is DNA, it can recombine with the chromosomes to produce transformant cells.

The present invention also provides a method for conferring resistance to stripe rust in a cereal crop plant, said method comprising transforming said plant with a vector or nucleic acid molecule according to the present invention. In one embodiment, the cereal crop plant is wheat.

In addition, the present invention provides a cereal crop plant, having stably incorporated into its genome a vector or nucleic acid molecule according to the present invention. In one embodiment, the cereal crop plant is wheat.

As described herein above, and in accordance with the present invention, the gene encoding for the WKS1 protein may give rise to six variant polypeptides due to alternative splicing. Thus, the present invention particularly relates to a transgenic wheat plant having stably incorporated into its genome a nucleic acid molecule comprising a nucleotide sequence selected from SEQ ID NO: 9 to 14. In one embodiment, the nucleic acid is of SEQ ID NO: 9.

The invention will now be illustrated by the following non-limiting examples:

EXAMPLES Example 1 Cloning of the High-Temperature Stripe Rust Resistance Gene Yr36

We report here the positional cloning of the high-temperature stripe rust resistance gene Yr36. This gene was first discovered in wild emmer wheat (T. turgidum ssp. dicoccoides accession FA15-3) (DIC) (Uauy et al., 2005). Analysis of Yr36 isogenic lines in different genetic backgrounds confirmed that this gene confers partial resistance to PST under field conditions, and is associated with significant yield increases when the pathogen is present. In controlled environments, plants with Yr36 are resistant at relatively high temperatures (25-35° C.) but susceptible at lower temperatures (e.g. 15° C.) (Uauy et al., 2005). Yr36 resistance, originally discovered in adult plants, has some effectiveness in seedlings at high-temperatures (FIG. 1). The wheat—P. striiformis interaction differs in juvenile and adult plants. Part of the difference is due to changes in leaf anatomy. In younger leaves, a single infection event leads to fungus growth both between and across the veins giving rise to a wide lesion (FIGS. 1, A, B, E, and F). In contrast, in adult leaves a single infection event is primarily limited in growing between veins, which results in a “stripe” pattern of sporulation (FIGS. 1, C, D, G, and H).

In addition to this Yr36-independent developmental difference, there is also a Yr36-dependent difference between adult and juvenile plants. In juvenile resistant plants inoculated at the 1^(st) leaf stage, necrotic patches appeared a few days later than the necrotic stripes observed in adult plants inoculated at later stages. Consequently, in some juvenile leaves, profuse sporulation was observed before any necrosis was detected (FIG. 1E).

Later, necrotic patches encompassed the region with pustules and limited the growth of the pathogen, i.e., there was no further expansion of the region of sporulation (FIG. 1, E and F, see also FIG. 10). These necrotic regions were not observed in susceptible UC1041 plants at comparable developmental stages (FIG. 1, A and B). The Yr36 resistance response at juvenile stages differs from a hypersensitive response in the delayed appearance of the necrotic regions and the incomplete control of sporulation within these necrotic patches.

Other high-temperature non race-specific resistance genes have provided durable resistance to stripe rust and are used frequently in wheat breeding programs.

To clone Yr36, we crossed the susceptible durum wheat variety Langdon (LDN, FIG. 2A) with the resistant isogenic recombinant substitution line RSL65 (FIG. 2B), which carries Yr36 in a LDN genetic background. We screened a population of 4500 F2 plants using Yr36 flanking markers Xucw71 and Xbarc136 (Uauy et al., 2005) and identified 121 lines with recombination events between these two markers. Based on genes from the rice colinear region, nine PCR markers were developed to construct a high-density map of Yr36 (FIG. 2, C and D, Table 2). Using replicated field trials and controlled environment inoculations (Tables 3 and 4, FIGS. 3 and 4), Yr36 was mapped to a 0.14 cM interval delimited by markers Xucw113 and Xucw111 (FIG. 2D).

Screening the RSL65 BAC library (Cenci et al., Theor. Appl. Genet. 107, 931, 2003) with the distal marker Xucw113 yielded six BACs (FIG. 5). BAC ends were used to re-screen the library and extend the contig by chromosome walking. BAC-end marker Xucw127 (Table 2, FIG. 5) was mapped proximal to Yr36, thereby completing the physical map (FIG. 2E). BAC clones 391M13 and 1144M20 were sequenced and a contiguous 314-kb sequence including the flanking markers was annotated and deposited in GenBank (EU835198, FIG. 6). New markers were developed from the sequence (Table 2) and Yr36 resistance (eight PST races, Table 5) was mapped between Xucw129 and Xucw148 (0.02 cM).

This region has two pairs of duplicated genes (FIG. 6). The first pair includes two short putative genes (IBR1 and IBR2) with an ‘in between RING finger’ domain (IBR, pfam01485). The two other duplicated genes, which we designated WHEAT KINASE-START 1 and 2 (WKS1 and WKS2, FIG. 2F), encode 86% identical proteins that have a predicted kinase domain followed by a predicted steroidogenic acute regulatory protein-related lipid transfer domain (START, pfam01852). WKS1, WKS2 and IBR1 are deleted in the susceptible parent (FIG. 2E). The WKS genes were prioritized for functional characterization because their domains have been associated with plant responses to pathogens in other species (Dardick and Roland, 2006; Tang et al., 2005; Vorwerk et al., 2007).

Example 2 Functional Characterization of WKS1 and WKS2

Primers specific for WKS1 and WKS2 putative kinase and START domains (Table 6) were used to screen a population of 1,536 ethyl methanesulphonate (EMS) mutagenized M2 lines from the common wheat breeding line UC1041+Yr36 (see Materials and Methods). Of the 117 mutants found in the TILLING screen (McCallum, L. Comai, E. A. Greene, S. Henikoff, Nat. Biotechnol. 18, 455, 2000), we selected for functional characterization 6 mutants with changes in conserved amino acids in WKS1 (FIGS. 7 and 8) and 3 with premature stop codons in WKS2 (Table 7).

Of the 6 WKS1 mutants, 5 showed susceptible reactions similar to the susceptible UC1041 control line (FIG. 9, panels A to F, and FIGS. 10 and 11). In contrast, none of the WKS2 truncation mutants was susceptible (FIG. 10), suggesting that WKS1 is Yr36. Both the kinase (FIG. 10) and START domains (FIG. 11) were necessary for the resistance response. For example, the T6-567 mutant had a susceptible response similar to UC1041 (null Yr36) and was more susceptible than its sister control line. This result indicates that a functional START domain in WKS1 is necessary for stripe rust resistance. Similarly, the T6-569 mutant and three other mutants having mutations in the kinase region had a susceptible response (Table 7). Laser point scanning confocal microscopy showed that the T6-312 mutant had an unrestricted network of fungal growth, whereas the control line with a functional WKS1 gene had a resistance response inside the leaf with reduced fungal growth delimited by autofluorescing plant cells (FIG. 9, panels G to J).

Example 3 Transformation of a Susceptible Wheat Variety with WKS1 Confer Resistance to Stripe Rust

To confirm the identity between WKS1 and Yr36, we transformed the susceptible wheat variety ‘Bobwhite’ with a 12.2-kb genomic fragment that includes the complete WKS1 coding and flanking regions (see Materials and Methods). Only two of the nine independent T1 transgenic lines had complete WKS1 transcripts and they were both resistant to stripe rust (FIG. 12 and FIG. 13) demonstrating that WKS1 is Yr36. Transgenic 26b lines showed a stronger hybridization signal than transgenic 17a lines, suggesting higher copy number of the transgene. Lines 26b-6 and 26b-15 showed high transcript levels (13B) and strong resistance (13A).

Example 4 Characterization of Temperature and Time Dependency of WKS1 Expression

The cloning and sequencing of 56 full-length WKS1 cDNAs revealed six alternative transcript variants (WKS1.1-6, FIG. 14). WKS1.1 is the only variant with 11 exons coding for a complete START domain. WKS1.2-6 transcript variants do not include exon 11 and have an alternative polyadenylation signal located upstream from this exon. WKS1.2 transcripts continue beyond the GT splicing site after exon 10 until a stop codon 57-bp after this splicing site. WKS1.3 transcripts have an alternative GT splicing site located 4-bp after exon 8. This change in reading frame generates a premature stop codon in exon 9. WKS1.4 transcripts continue through the GT splicing site at the end of exon 8 until a stop codon in intron 8 (marked in red). WKS1.5 transcripts have a premature splicing site in exon 7 (56-bp before the conserved GT splice site, marked in red), which changes the reading frame and generates a stop codon within exon 8. WKS1.6 transcripts do not include the second exon (marked in red). This difference generates a change in reading frame and a premature stop codon in exon 3.

Several amino acids from the C terminal end of the START domain are well conserved from vascular plants to mosses. Deletions of the last 10 amino acids of the human StARD protein result in non functional proteins, indicating that this region is critical for its normal function. In the human START proteins, the C terminal α4 helix opens and closes the steroid binding pocket in the hydrophobic tunnel and is able to interact with lipid membranes. Therefore, it is possible that the elimination of the conserved C terminal region in WKS1.2-6 might alter or eliminate function (FIG. 8B).

Quantitative PCR showed that even the lowest transcript levels of WKS1.1 and WKS1.2-6 are only 3-fold lower than those of ACTIN, indicating relatively high transcript levels. Overall, high temperature up-regulates WKS1.1 (FIG. 15, panels A to C and FIG. 16) and down-regulates WKS1.2-6 (FIG. 15, panels D to F and FIG. 16) (P<0.0001, Table 8).

PST inoculation consistently down-regulated WKS1.2-6 across temperature and time, but the effect on WKS1.1 transcript levels varied with sampling times (FIG. 15, panels A to C). Comparisons between WKS1.1 and WKS1.2-6 transcript levels in PST-inoculated plants (FIG. 16, panels A to C) showed no significant differences at low temperature (susceptible response, P>0.55), and significantly higher values of WKS1.1 relative to WKS1.2-6 at high temperature (resistant response, P<0.01) for all three days.

The relative increase in transcript levels of the variant with the complete START domain (WKS1.1) at high temperature parallels the observed high-temperature resistance conferred by Yr36. START domain proteins in humans are known to play important roles in lipid trafficking, metabolism and sensing, and their binding with sterols and ceramides result in protein conformational changes. If the putative WKS1 START domain has the ability to bind lipids from, or redirected by PST at high-temperature and change its conformation, this may cause the kinase domain to initiate a signaling cascade leading to the observed programmed cell death (FIG. 9 and FIG. 10). The WKS1 Ser/Thr kinase domain (pfam00069) was confirmed to have kinase activity (FIG. 17).

Kinase fusion protein was confirmed by Western blot using a GST-antibody and by peptide sequencing of the ˜66-kD protein band (WKS1-Kinase protein sequence coverage was >91%). The Western blot also shows that the strong band of ˜28 kD in the GST-WKS1_Kinase construct (white arrow) has the GST protein and is likely the result of partial cleavage of the GST-WKS1Kinase fusion protein in E. coli. As expected, this cleaved protein did not show kinase activity (FIG. 17, panel B). The ˜80-kD protein band present in both KIN and GST is the E. coli chaperone protein HSP70 that is known to have kinase activity (FIG. 17, panel B) but lacks GST (FIG. 17, panel C). This experiment was repeated with identical results.

Discussion.

The combination of the kinase and START domains in WKS1 apparently is the result of a novel domain shuffling because these two domains are not found together in other organisms. The most similar protein in Arabidopsis to the putative WKS1 START domain is EDR2, a protein that negatively regulates plant defense to the powdery mildew pathogen Golovinomyces cichoracearum (12, 13). EDR2 has a PH (pfam00169) and a DUF1336 (pfam07059) domain, which are absent in WKS1. The WKS1 kinase has high similarity to several Arabidopsis WAK-like kinases (FIG. 7), but WKS1 lacks the additional domains characteristic of WAK-like kinases. The WKS1 kinase belongs to the non-RD kinases, which are frequently involved in the early steps of the innate immune response.

The appearance of this novel gene architecture preceded the origin of the Triticeae since WKS1 and WKS2 were detected in several species from this tribe (Table 9, FIG. 18). However, the presence of these two genes was rare among Triticeae species and varied across accessions within those species where they were detected. This suggests that WKS1 and WKS2 were lost repeatedly in several grass lineages, including the diploid donors of the A and D genomes of polyploid wheat (Table 9). Amongst 131 wild and cultivated tetraploid wheat accessions, WKS1 was detected only in wild wheat (24% of accessions) suggesting that WKS1 was not incorporated into the initial domesticated forms. In hexaploid wheat WKS1 was present only in five accessions where the DIC segment (see item 1 of Materials and Methods) was incorporated recently (Table 10).

Introgression of WKS1 in transgenic Bobwhite wheat and in susceptible varieties by backcrossing (Uauy et al., 2005) improved their resistance to stripe rust. This indicates that either WKS1 is sufficient to improve resistance, or that WKS1 can trigger intermediate genes that initiate the hypersensitive response, and that these genes are still present in the tested varieties. This, together with the absence of WKS1 in almost all modern commercial varieties of pasta and bread wheat (Table 10), suggests that the introgression of Yr36 could have a broad impact in improving resistance to this pathogen. Yr36 resistance has remained effective against the numerous stripe rust races present in California (2004 2008 field tests) and to all races tested so far in controlled environments (Table 5). Moreover, Yr36 has improved resistance in a variety carrying the non race-specific Yr18 resistance gene (Uauy et al., 2005), which suggests that pyramiding appropriate combinations of non race-specific resistance genes may provide adequate resistance against this pathogen. The discovery of different proteins and resistance mechanisms for non-race specific resistance genes Yr36 and Yr18/Lr34 (Schrick et al., 2004) suggests that this type of resistance may involve a heterogeneous group of genes and mechanisms.

Materials and Methods.

Gene sequences have been deposited in GenBank with accession numbers: EU835198-EU835200, FJ154103-FJ154118 and FJ155069-FJ155070.

1.—Plant Materials and Growing Conditions for Rust Bioassays

Mapping: The mapping population was developed from a cross between the tetraploid wheat (Triticum turgidum L ssp. durum) cv. Langdon (LDN) and RSL65, a near isogenic line of LDN with a 30-cM segment of chromosome arm 6BS from T. turgidum L. ssp. dicoccoides (accession FA15-3, designated as DIC hereafter) (1).

Targeted Induced Local Lesions IN Genome (TILLING): The TILLING population was developed using the hexaploid wheat (T. aestivum L.) breeding line UC1041+Yr36. UC1041 is a hexaploid spring breeding line derived from the cross Tadinia/Yecora Rojo. The DIC 6BS segment including Yr36 was introgressed from the wheat variety Glupro (I. A. Khan et al., Crop Sci. 40, 518 (2000) followed by six backcrosses into UC1041. UC1041 is susceptible to Puccinia striiformis f. sp. tritici (PST) race PST-113, which is virulent on the Yr1 resistance gene present in UC1041. Seeds from UC1041+Yr36 were mutagenized with 1% ethyl methane sulphonate (EMS) and M2 plants were produced from independent M1 mutants. DNAs were extracted from 1,536 M2 lines and organized in 384 4-fold DNA pools that were screened using TILLING (C. M. McCallum, et al., Nat. Biotechnol. 18, 455, 2000).

Transgenics: The hexaploid spring wheat variety ‘Bobwhite’ was used for the transgenic complementation experiment. This variety is susceptible to PST-113.

Growing conditions and inoculation stages: All the chamber experiments used long day photoperiod (8 h dark, 16 h light). For the stripe rust inoculations in the controlled environment experiments, plants were placed in a dew chamber without light at 10° C. for 24 h. Plants were inoculated either at the 1-4 leaf stage (“seedling inoculation”) or after flag leaves were fully emerged (“adult-plant inoculation”) (FIG. 1). Plants were then moved to one of two different temperature regimes, both of which induce the expression of Yr36 resistance. The first one had a gradual change between a minimum of 10° C. at the middle of the dark period to a maximum of 35° C. at the middle of the light period (referred hereafter as 10/35° C.). This treatment was effective for the expression of Yr36 resistance in different genetic backgrounds. In the second temperature regime, plants were kept at constant 10° C. during the dark period and at constant 25° C. during the light period (referred hereafter as 10/25° C.). This treatment was also effective for the expression of Yr36 resistance (FIG. 1). When indicated, other conditions were used as described in the Materials and Methods.

In all experiments pots were randomized during infection and disease development. Plants were scored blind by two independent evaluators and either photographs or scans were taken to document the results.

Field tests were conducted in Davis (2006, 2007, and 2008) and organized in a complete randomized design (CRD, 2006 and 2007) or a randomized complete block design (RCBD, 2008). All field experiments included a border of “spreader rows” of the highly-susceptible wheat variety D6301 which was used to spread inoculum. One meter rows were used as experimental units. Seeds were sown in November and plants inoculated with PST-100, a race predominant throughout the US, were planted in the spreader rows in March. Additional races were likely present since severe natural infections were observed across the field in all three years. Infection severity was recorded twice from May to early June.

2.—Stripe Rust Races, Inoculation Procedures, and Confocal Images

Table S1 describes the PST races, their virulence profiles and the year they were first described. The PST races used in this study included some of the most virulent and predominant races from 2000 to 2007 in the U.S. For inoculation, urediniospores were mixed with laboratory-grade talcum powder (Fisher Scientific, Fairlawn, N.J., USA) and dusted on the leaf tissue. Rust severity was evaluated two to three weeks after inoculation using a 0-9 scale of infection type (IT) (R. F. Line, Technical Bulletin 1788 (United State Department of Agriculture, 1992): 0-3 (resistant, none to trace level sporulation), 4-6 (intermediate, light to moderate sporulation), 7-9 (susceptible, abundant sporulation). Alternatively, for the mapping and TILLING experiments, the percentage of leaf surface covered with PST pustules was quantified using the digital image analysis program “pd” (FIG. 3).

Confocal methods: Wheat leaves were processed for fluorescence microscopy as published before (J. Moldenhauer et al., Plant Pathol. 55, 469, 2006). The uvitex-stained leaves were examined first with a Nikon Microphot SA fluorescence microscope with a UV-2A DM 400 filter (Nikon, Melville, N.Y., USA). Images shown in FIG. 9, panels G to J, were taken on a laser point scanning confocal microscope (Olympus FV1000 spectral scanner with an UPLAPO 40′ oil objective N.A. 1.0). Tissue was sequentially scanned with lasers at 405 and 543 nm to detect uvitex and autofluorescence, respectively. The laser power at 405 nm was reduced five-fold in the compatible interaction because of the greater concentration of uvitex-stained fungus. Each image is comprised of a z-series of 98 sections at 1.2 μm steps with a 0.124 μm per pixel resolution.

3.—High-Density Genetic Map

A total of 4,500 F2 plants from the cross LDN′RSL65 were screened for recombination between PCR markers Xucw71 and Xbarc136 (1) (FIG. 2) and 121 lines were selected (Table 3). Selected plants were self-pollinated and recombinant substitution lines (RSLs) homozygous for the recombinant chromosomes were obtained.

Wheat ESTs with homology to single or low copy number genes in the colinear region in rice (FIG. 2, Table 2) were used to develop additional PCR markers and to further characterize the 121 critical RSLs (Table 3). Briefly, primer pairs were designed for conserved regions between rice and wheat ESTs and were used to amplify predicted introns in LDN and RSL65. PCR products were cloned into the pGEM-T vector (Promega, Madison, Wis., USA). Clones from the A and B genomes were differentiated by restriction enzyme fingerprinting. Products from each genome were sequenced and polymorphisms between LDN and RSL65 were used to develop markers (Table 2). Additional markers were developed from Bacterial Artificial Chromosome (BAC) ends and BAC sequences generated during the construction of the physical map.

Seventy RSLs representing all the different recombination events present in the 121 critical lines (Table 3) were evaluated for adult plant resistance to PST-100 at 10/35° C. Thirty six RSLs were also evaluated for adult plant resistance in the field during 2006 at UC Davis. A summary of the host-pathogen interaction phenotype is presented in Table 3. To validate the mapping of Yr36, the 13 RSLs with the closest recombination events (0.14-cM interval between Xucw111 and Xucw113) were retested for resistance to PST-100 in different environmental conditions and growth stages (Table 4, FIG. 4).

An additional experiment using the same temperature conditions (10/35° C.) was performed using eight different PST races that are virulent on LDN (Table 1). The experiment included control lines LDN and RSL65 and five recombinant lines with the closest recombination events flanking Yr36 (RSL241, RSL402, RSL504, RSL1747, RSL39-14; Table 5).

4.—Physical Map

The physical map of the Yr36 region was constructed using the BAC library from the resistant parent RSL65 (A. Cenci et al., Theor. Appl. Genet. 107, 931, 2003) and a pooling PCR screening strategy that was described before (A. Cenci et al., Genome 47, 911, 2004). The initial screening was performed using B-genome specific primers for the distal marker Xucw113 (Table 2). Six positive BAC clones (391M13, 400M22, 782M23, 85201, 1129G14, and 1217L2) were identified (FIG. 5).

The BAC end sequence of clone 1129G14 was used to generate the single copy marker Xucw125 (Table 2), which is absent in LDN and present in RSL65. This marker was mapped proximal to Xucw113 and completely linked to Yr36, which oriented the contig formed by these 6 BAC clones relative to the genetic map. Screening of the BAC library with the Xucw125 primers generated four new positive clones (508C11, 528D22, 691B11, and 984G1; FIG. 5). The BAC-end sequence of BAC clone 508C11 was used to generate marker Xucw126 (Table 2), which also was absent in LDN and present in RSL65, and was completely linked to Yr36. Xucw126 was used to screen the BAC library and four new positive BAC clones were identified (651E2, 1046P23, 1070P18, and 1144M20, FIG. 5).

BAC-end sequencing of clone 1046P23 was used to generate marker Xucw127 (LDN: 110-bp and RSL65:105-bp, Table 2). The 5-bp polymorphism was mapped proximal to Yr36 (Table 3), which completed the physical map (FIG. 5). Xucw127 is part of a predicted pectin lyase-like gene with an X8 domain (pfam07983).

5.—Contig Sequencing and Delimitation of the Yr36 Candidate Region

Overlapping BAC clones 391M13 and 11441v120 were sequenced and a 314,057-bp contig was generated, annotated, and deposited in GenBank (EU835198, 7.5-fold coverage at Phred: 20). This sequence includes the proximal region of BAC 391M13 and the complete sequence of BAC 1144M20. The annotated contig includes the complete 186-kb Yr36 region flanked by markers Xucw129 and Xucw148.

The proximal recombination event in RSL504 occurred between the DIC IN BETWEEN RING finger1 (pfam01485) IBR1 and LDN IBR2 genes as confirmed by sequencing (FJ155069 and FJ155070). Based on the location of this recombination event the promoter and proximal 250-bp of the IBR1 gene were excluded from the Yr36 candidate gene region.

Over 80% of the sequence was identified as repetitive using the Triticeae Repeat Sequence Database (TREP http://wheat.pw.usda.gov/ITMI/Repeats/index.shtml) and the TIGR Cereal Repeat Database (http://tigrblast.tigr.org/eukblast/index.cgi?project=tae1). The non-repetitive sequence was annotated using BLAST searches in GenBank, the wheat EST collection at GrainGenes (http://www.graingenes.org/) and the TIGR Wheat Genome Database (http://tigrblast.tigr.org/euk-blast/index.cgi?project=tae1), and the gene prediction programs Genscan (http://genes.mit.edu/GENSCAN.html) and FGENESH (http://www.softberry.com/berry.phtml) (FIG. 6).

6.—TILLING Mutants

The UC1041-1-Yr36 mutant population was screened for mutations in two regions of WKS1 and WKS2. The first one included the complete kinase domain and was 1,371 bp and 1,460-bp in WKS1 and WKS2, respectively. The second region included part of the START domain (pfam01852) and was 1,270-bp and 1,532-bp in WKS1 and WKS2, respectively. The targeted WKS regions were selected using the CODDLE program (http://www.proweb.org/coddle/), which helps Choose codons to Optimize the Detection of Deleterious Lesions. Primers specific for each of these region (Table 6) were used to screen 1,536 DNAs for WKS1 and 768 for WKS2. Using the PARSESNP and Blockmaker programs (http://www.proweb.org/Tools), we selected mutations that were predicted to have the strongest effect based on Position-Specific Scoring Matrix (PSSM) differences and Sorting Intolerant From Tolerant (SIFT) scores (P. C. Ng, S. Henikoff, Genome Res. 11, 863, 2001), or that led to premature truncations (Table 7).

For each mutation, M3 plants homozygous for the mutant alleles were selected. For WKS1 lines T6-312, T6-138, and T6-567, and for WKS2 line T6-826, M3 plants homozygous for the non-mutant alleles were also selected as additional controls (FIGS. 9 to 11). Resistance to race PST-113 was evaluated at 10/25° C. in three separate experiments that included different mutants and controls as they became available.

Mutant experiment 1: In this experiment plants were inoculated at the 4th-leaf (juvenile) stage. Fifteen days after inoculation the edge of the areas covered with pustules was marked with a black line. Five days later the same leaves were scanned to evaluate the progression of the disease beyond the mark (FIG. 10). When pustules were restricted to the marked area, plants were considered resistant and when they spread beyond the marked border they were considered susceptible (FIG. 10).

Mutant experiment 2: In this experiment we retested WKS1 mutant lines T6-138 and T6-312, their corresponding non-mutant sister lines, and the susceptible and resistant control lines for PST resistance at the flag leaf (adult) stage. The percent of leaf area covered by pustules was quantified in eight leaves per line using the pd program (FIG. 3). Percentage area was log-transformed to achieve homogeneity of variance and differences were tested using ANOVA (FIG. 9). Images in FIG. 9 were obtained from plants used in this experiment.

Mutant experiment 3: The third experiment was performed to test mutant line T6-567 (discovered later), which has a mutation in the START domain affecting a conserved amino acid (FIG. 8A). Sister lines homozygous for the presence and absence of this mutation were compared for resistance to race PST-113 at the elongation (adult) stage (FIG. 11). Lines UC1041 and UC1041+Yr36 were included as additional, controls.

7.—Complementation Using Transgenic WKS1 Plants

To confirm that WKS1 confers partial resistance to stripe rust, we transformed the susceptible common wheat variety Bobwhite with the pWKS1 plasmid, which includes the complete WKS1 gene. We used the High-Fidelity DNA Polymerase Phusion™ enzyme (Finnzymes, Espoo, Finland) to amplify a 12,205-bp genomic DNA fragment from RSL65 by PCR. SbfI and NotI restriction sites were added to the primers for cloning (YR36_S1F1/S1R4, Table 6). This fragment included 3,503-bp upstream from the WKS1 start codon, the complete WKS1 coding region, and 1,415 bp downstream from the stop codon.

The PCR product was cut by restriction enzymes SbfI and NotI, recovered from a 1% agarose gel, and cloned into a SbfI-NotI linearized pGEM®-T vector (Promega, Madison, Wis., USA). To reduce the frequency of breaks within the coding sequence during transformation, the previous construct was digested with SbfI and further cloned into a SbfI linearized pPZP201 vector to increase the size of the non-genic region (the pWKS1 final construct is ˜22.3-kb). The nucleotide sequence of pPZP201 vector is disclosed in P. Haidukiewicz, Z. Svab, P. Maliga, Plant Mol. Biol. 25, 989 0994). The WKS1 region (12,205-bp) was sequenced and showed no differences with the wild type allele. Embryonic calluses of hexaploid spring variety Bobwhite were bombarded using a 1:1 molar ratio of pWKS1 and UBI::BAR selectable marker plasmids (15.5 μg total) coated onto Seashell 1000 nm gold particles (La Jolla, Calif., USA), according to the manufacturer's instructions. Transformants were selected as previously described (C. Uauy, A. Distelfeld, T. Fahima, A. Blechl, J. Dubcovsky, Science 314, 1298, 2006).

In total, nine independent transgenic T1 lines were obtained and positive plants were confirmed by PCR using primer pair YR36_(—)13104F/13692R (Table 6). Transcription of the full length WKS1 gene in the transgenic T1 plants was confirmed by reverse transcriptase PCR(RT-PCR) using WKS1 transcript specific primers WKS1_(—)150F, 151R, and 174R (Table 6). Of the nine transgene-positive lines, only 17a and 26b yielded full-length WKS1 cDNAs and were used for functional studies. Transcript levels of the WKS1 transgene (all transcript variants) were determined by real-time quantitative PCR (Q-PCR) with primers WKS1_F1/R1 (Table 6) before PST inoculation. Transgenic and control lines were tested for PST resistance with race PST-113, which is virulent on Bobwhite (FIG. 3 and FIG. 13A).

Southern blots including DNAs digested with HindIII from eight 17a T1 plants and seven 26b T1 plants were hybridized with a 942-bp WKS1 fragment derived from PCR primers YR36_PF/PR (Table 6). Radioactive probes were prepared with Prime-a-Gene® Labeling System (Promega, Madison, Wis., USA) and purified by MicroSpin™ G-50 columns (Amersham, Piscataway, N.J., USA). Three 17a T1 plants showed no transgene insertion and were retained as additional negative controls (FIG. 13). The construct has two HindIII sites flanking the probe region so a fragment of similar size is expected in different transgenic events (blue arrow, FIG. 13). Pre-hybridization, hybridization, and washing were performed as described before (Dubcovsky et al., Theor. Appl. Genet. 87, 957, 1994).

8. —WKS1 transcription

WKS1 alternative transcript variants (WKS1.#). Sequencing of 56 cDNA clones amplified with poly T primer and/or WKS1 specific primers showed six alternative transcript variants (WKS1.1-6, FIG. 14). These six variants were classified into two groups based on the presence or absence of exon 11, the last exon. Transcript variant WKS1.1 included the complete gene with the poly A sequence starting 80-bp after the stop codon in exon 11. For transcript variants WKS1.2-6 the poly A tail started 80-95 bp downstream of the splicing site of exon 10, approximately 1,450-bp upstream from the start of exon 11. As a result of the exclusion of exon 11, WKS1.2-6 variants encode for shorter proteins with a truncated START domain (FIG. 14).

For the Q-PCR experiments, primers WKS1_F5/R5 were used to amplify transcript variant WKS1.1 and primers WKS1_F4/R4 to amplify transcript variants WKS1.2-6 (Table 6). The reverse primer was unique to each group with WKS1_R5 annealing to the splice junction of exons 10 and 11 (unique for WKS1.1) and WKS1_R4 annealing to the unique WKS1.2-6 sequence of exon 10 that is missing from WKS1.1 (FIG. 14). Conserved primers WKS1_F1/R1 were used to amplify simultaneously all six transcript variants (Table 6).

Real-time quantitative PCR(Q-PCR). Total RNA was extracted using TRIZOL (Invitrogen, Carlsbad, Calif., USA) and first strand cDNA was synthesized using the SuperScript™ First-Strand Synthesis System (Invitrogen, Carlsbad, Calif., USA). Q-PCR was performed on an ABI PRISM 7000 SDS (Applied Biosystems, Foster City, Calif., USA) using SYBR® GREEN. PCR setup and reaction conditions were as reported before (Fu et al., Mol. Gen. Genomics 277, 301, 2007). The 2^(−ΔΔCT) method (Livak and Schmittgen, Methods 25, 402, 2001) was used to normalize and calibrate transcript values relative to the endogenous ACTIN control (Table 6).

Efficiencies of each pair of primers were calculated using six 2-fold dilutions (1:1, 1:2, 1:4, 1:8, 1:16 and 1:32) in triplicates. Amplification efficiencies were higher than 95% for all three systems. The same calibrator was used for all transcript variants within each experiment so their values are comparable (2^(−ΔΔCT) values represent number of RNA copies per copy in the calibrator sample).

Effect of temperature, PST inoculation, and days post inoculation (DPI) on WKS1 transcript levels. Tetraploid RSL65 (resistant parental line in the mapping population) was used for this experiment. Seedlings were initially grown at a low temperature regime, which was constant 10° C. during the 8 h dark period and constant 15° C. during the 16 h light period. Half of the plants were kept at low temperature and the other half were moved to the 10/35° C. temperature cycle. Chambers for all treatments were maintained at the same photoperiod (16 h of light and 8 h dark) and light intensity (145 μmol m⁻² s⁻¹). In all cases, samples were collected between noon and 1:00 pm.

Plants at the three-leaf stage within each temperature treatment were divided in two groups. The first group was inoculated with PST-100 and the other group was used as non-inoculated control. Six samples were collected 3, 9, and 16 days after inoculation for each of the four treatment combinations (total 72 samples). The effects of temperature, PST inoculation, days after inoculation, and their respective interactions on WKS1.1 and WKS1.2-6 transcript levels were analyzed using three-way factorial ANOVAs. Since there was a significant three-way interaction between temperature, inoculation and DPI, we analyzed separately the effect of temperature and inoculation at 3, 9 and 16 DPI. Results are summarized in FIG. 15 and FIG. 16 and in Table 8.

9.—Distribution of the WKS1 and WKS2 Genes Among Different Triticeae Species.

Samples for the Triticeae species were generously provided by Dr. J. Dvorak (University of California Davis, USA, DV numbers Table 9), the University of Haifa (Israel) germplasm collection and the USDA National Small Grain Collection (NSGC Aberdeen, Id.) (Table 9). The accessions of wild emmer (Table 10) were from the University of Haifa collection and from the USDA-NSGC. T. turgidum ssp. dicoccum accessions were from the USDA-NSGC. Durum and bread wheat accessions were kindly provided by M. C. Sanguineti (Bologna University, Italy) or were from the UC Davis collection.

PCR conditions and sizes of the amplified products are described in the legend of FIG. 18 and primer sequences are shown in Table 6.

Primers for the kinase domain amplify fragments of 128-bp for both WKS1 and WKS2 (see Example 2). These primers require an initial touchdown with a decrease of 0.5° C. per cycle from 70 to 66° C. (30 s per cycle). Two pairs of primers, each specific for one of the WKS genes, were used to determine the presence of the inter-domain region. The first one amplifies a product of 733-bp when WKS1 is present and no product in its absence. The second inter-domain primer pair amplifies a product of 694-bp when WKS2 is present and no product when it is absent. These primers require an initial touchdown with a decrease of 0.5° C. (60 s) per cycle from 65 to 60° C. for the first pair and from 64 to 59° C. for the second pair (60 s per cycle). The primer pair specific for the START domain amplifies products of 871-bp from WKS1 and 537-bp from WKS2. Size differences are partially due to the insertion of a miniature inverted repeat transposable elements (MITE) in the WKS1 intron amplified by these primers. These primers require an initial touchdown with a decrease of 0.5° C. per cycle from 70 to 65° C. (60 s per cycle).

10.—In-Gel Kinase Assay

Plasmid construction: A GST fusion construct including the complete kinase domain (WKS1 amino acids 1-332, GenBank accession EU835199) was developed for the kinase activity assay. This sequence was PCR amplified from cDNA using primers GST_EcoRI_F1 and GST XhoI_R1 (Table 6) and initially cloned into pGEM-T Easy vector (Promega, Madison, Wis., USA). Restriction enzymes EcoRI and XhoI were used to clone this fragment into expression vector pGEX-6P-1 (GE Healthcare, Piscataway, N.J., USA), resulting in construct GST-WKS1_Kinase. Sequencing confirmed that no PCR errors were introduced.

Expression and purification of fusion proteins: GST-WKS1_Kinase was transformed into E. coli strains pLysS (Gene Choice, Frederick, Md., USA) and BL21(DE3). Bacteria were grown in 50 mL of LB media containing ampicillin (100 μg/ml) to O.D.₆₀₀ of 0.6-0.8. Before induction of the fusion protein, cells were collected by centrifugation at 5000 rpm for 5 minutes. Cells were resuspended in 50 mL of fresh LB media containing ampicillin (100 μg/ml) and 1 mM of isopropyl-1thio-p-D-galactopyranoside (IPTG) and incubated at 37° C. for 6-8 hours. Cells were harvested by centrifugation and resuspended in 1×PBS buffer (137 mM NaCl, 2.7 mM KCl, 4.3 mM Na₂HPO₄, 1.47 mM KH₂PO₄, pH 7.4) supplemented with Complete Protease Inhibitor Cocktail Tablets (Roche, USA) and lysozyme (Sigma-Aldrich, St. Louis, Mo., USA). The resuspended cells were lysed by sonication and the lysate was centrifuged at 5000 g for 5 m. The GST-fusion protein was purified using glutathione-Sepharose 4B (GE Healthcare, Piscataway, N.J., USA) according to manufacturer's instructions and dialyzed overnight against 50 mM HEPES-NaOH, pH 7.4, using the Mini Dialysis Kit (GE Healthcare, Piscataway, N.J., USA).

In-gel kinase assays: In-gel kinase assays were performed as described by Romeis et al. (Romeis et al., Plant Cell 11, 273, 1999) except that the SDS-PAGE gel was co-polymerized with casein (1 mg/ml, C4032, Sigma-Aldrich, St. Louis, Mo., USA) as the phosphorylation substrate and a different kinase buffer was used. The kinase buffer included 50 mM HEPES-NaOH, pH 7.4, 10 mM MgCl2, 10 mM MnCl2, 1 mM DTT, phosphatase inhibitors (pglycerophosphate, NaF, Na3VO4; Cayman Chemical, Ann Arbor, Mich., USA) and 75 μCi of [γ-³²P]ATP (6000 Ci/mmol, Perkin Elmer Life Sciences, Boston, Mass., USA. Gels were analyzed using a Storm 860 PhosphorImager (GE Healthcare, Piscataway, N.J., USA). The size of the phosphorylated proteins was estimated by using a prestained molecular mass marker.

Peptide Sequencing: To confirm the identity of the induced GST-WKS1_kinase fusion protein, we prepared the protein corresponding to the ˜66-kD band for MS analysis using standard reduction, alkylation, and tryptic digest procedures (Rosenfeld et al., Anal. Biochem. 203, 173, 1992). Digested peptides were analyzed by LC-MS/MS on an LTQ with Michrom Paradigm LC and CTC Pal autosampler at the UC Davis Genome Center Proteomics Core Facility (http://proteomics.ucdavis.edu/). All MS/MS samples were analyzed using Sequest (ThermoFinnigan, San Jose, Calif.; version SRF v. 3) to search a custom database assuming the digestion enzyme trypsin. Scaffold (version Scaffold_(—)2_(—)01_(—)01, Proteome Software Inc., Portland, Oreg.) was used to validate MS/MS based peptide and protein identifications.

Western blots. GST-WKS1_kinase and GST proteins were transferred to Amersham Hybond™ ECL™ membranes by a vertical blotting unit using protein transfer buffer (1L: 3.03 g Trizma base, 14.4 g Glycine, 200 ml Methanol, pH 8.3). The presence of GST was tested using a rabbit GST antibody and detected using the ECL plus Western Blotting Detection System (Amersham Bioscience, Buckinghamshire, UK).

REFERENCES

-   Dardick, P. Ronald, PLOS Pathog. 2, 14 (2006). -   Schrick, Nguyen, W. M. Karlowski, K. F. X. Mayer, Genome Biol. 5,     (2004) -   Singh, H. M. William, J. Huerta-Espino, G. Rosewarne, Proc. 4 Int.     Crop Science Congress, Brisbane, Australia, 26 Sep.-1 Oct. (2004). -   Tang, J. Ade, C. A. Frye, R. W. Innes, Plant J. 44, 245 (2005). -   Uauy et al., Theor. Appl. Genet. 112, 97 (2005). -   Vorwerk et al., BMC Plant Biology 7, 1 (2007).

Tables

TABLE 1 Races of PST used in seedling and adult plant resistance tests. Year Races Susceptible wheat differential genotypes¹ isolated PST-17 1, 2, 3, 9, 11. 1977 PST-37 1, 3, 6, 8, 9, 10, 11, 12. 1987 PST-45 1, 3, 12, 13, 15. 1990 PST-100 1, 3, 8, 9, 10, 11, 12, 16, 17, 18, 19, 20. 2004 PST-113 1, 2, 3, 8, 9, 10, 11, 12, 14, 16, 17, 18, 19, 20. 2004 PST-116 1, 3, 4, 5, 8, 9, 10, 11, 12, 14, 16, 17, 18, 19, 20. 2005 PST-127 1, 2, 3, 5, 6, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 19, 2007 20. PST-130 1, 3, 4, 8, 10, 11, 12, 16, 17, 18, 19, 20. 2007 ¹Numbers indicate the wheat differential genotypes used to identify the race: 1 = Lemhi, 2 = Chinese 166, 3 = Heines VII, 4 = Moro, 5 = Paha, 6 = Druchamp, 8 = Produra, 9 = Yamhill, 10 = Stephens, 11 = Lee, 12 = Fielder, 13 = Tyee, 14 = Tres, 15 = Hyak, 16 = Express, 17 = Avocet S + Yr8, 18 = Avocet S + Yr9, 19 = Clement, and 20 = Compair.

TABLE 2 PCR markers used to produce the genetic map. Markers are listed from the telomeric to the centromeric location. Ann. Ext. Rest. Polym. Locus Marker Primers SIN (° C.)¹ (s)¹ Enz.1 (bp)¹ Rice homolog Xucw110² CAPS³ GGAGCAGCCACATCGTCG 16 57⁵ 210 MspI L⁴ ≅ 2000 Os02g0139200 GCCTGCTCCAACAACCATC 17 Xucw70 CAPS GTCTGTCCATGGGTTCTC 18 57⁵ 180 DpnII L ≅ 1850 Os02g0139300 GTCATGAAGCCTTGGTTGAAG 19 D ≅ 850 Xucw112 CAPS GGAGTGGAACCAGAGGAGC 20 57⁵ 120 HaeIII L ≅ 390 Os06g0703500 ATGATGTGCACCATGCGG 21 D ≅ 300 Xucw113 CAPS GCTGGAGGTGAGTGGTGAAT 22 57 30 TaqI L = 252 Os02g0139500 AATCTCCTCCCTTCGATGCT 23 D = 175 Xucw128 BACs³ TTAGATGGAGTCCCGTGGAG 24 58 40 none L ≅ 195 (wheat TGAAGCCAGCAATGAAGTTG 25 D = 189 genomic) Xucw129a² BACs AAGGACTCTGCTCCTGACGA 26 58 130 none D = 1452 (wheat GAAGATGCTCTGAACGCACA 27 genomic) Xucw129b² BACs AAGGACTCTGCTCCTGACGA 28 55 60 Tsp509I L ≅ 760 (wheat TGTCGAGGGACACAATACCA 29 genomic) Xucw125² BACe³ CAAGCGATGTCAACATGTCC 30 57 30 none D = 143 (wheat TCAAATGACAGCTCCACTCG 31 genomic) Xucw126² BACe GATGGTGCCTGCGATAATTT 32 57⁵ 180 none D = 2725 (wheat GCTGTCGACATTCCCCTAGA 33 genomic) Xucw130² BACs CACGCAAATAAATGCTGGTG 34 64 40 none D = 161 (wheat TGCATAGTTTCAGCCAGGTG 35 genomic) Xucw148² BACs CCCTTTGTGCCACATTTCTT 36 57⁵ 240 RsaI D = 462⁶ (wheat GGCAGGTGGAAGTCAACATT 37 genomic) Xucw127⁷ BACe GTACGTCCTGCTCACCATCA 38 65 30 none L = 110 (wheat AGAAGAACAACGGAGGACGA 39 D = 105 genomic) Xucw111 CAPS ACCCGTAAGATGCAATAACTTG 40 59 30 RsaI L ≅ 306 Os02g0139700 GCAGGACTGCTCTTGAAG 41 D = 215 Xucw69 dCAPS³ AGTTGTCATGTAATAGGTTGTA 42 45 30 SphI L = 140 Os02g0141300 CC ATACATCAGTATKTATGTGGCA 43 D = 120 TG^(8,9) Xucw103 dCAPS CTTTGTTTCCTGTATACGAATG 44 45 30 PstI & L = 217 Os02g0142500 CTTT⁸ XmnI¹⁰ AGAAGAATTTACAAATACACAG 45 D = 239 C Xucw65 CAPS GCATGTTTCAGTTTGGTTATCA 46 53 40 NcoI L = 418 Os02g0146600 CTCATCATCACATCACAAAGGA 47 D = 684 A Xucw102 dCAPS AACATAAGAGGGAGGTCGAG 48 59 30 DraIII L = 205 Os02g0148600 GAACAAGAGCACAGCACGTTGT⁸ 49 D = 188 ¹Ann.: annealing temperatures, Ext.: extension time, Rest. Enz.: restriction enzyme, and Polym.: polymorphic band size. ²Dominant marker. ³CAPS: Cleavage Amplified Polymorphic Sequences, dCAPS: degenerate CAPS (Michaels and Amasino, Plant J. 14, 381 (1998).), BAC_(e): BAC end sequence, BAC_(s): BAC sequence. ⁴L: Langdon; D: T. turgidum ssp. dicoccoides accession FA15-3. ⁵Initial touch-down: 8 cycles of decreasing 1≅ C. steps from 65° C. to 57° C. ⁶The amplification product is 2.68-kb and the polymorphic digested band is 462-bp. ⁷Xucw127 is part of a predicted pectin lyase-like gene with an X8 domain (outside Yr36 region). ⁸Underlined letters indicate degenerate nucleotides that were introduced to generate polymorphic restriction sites. ⁹The reverse Xucw69 primer includes a degenerate K nucleotide (G or T). ¹⁰Polymorphism is detected by XmnI, and PstI is used to reduce fragment size for convenient visualization in polyacrylamide gel

TABLE 3 Genotypes of the 121 recombinant substitution lines (RSLs) used for genetic mapping of Yr36. The 13 critical RSLs with the closest recombination events flanking Yr36 are indicated in bold, and their detailed phenotypic evaluation is presented in Table 4. Primers are listed in Table 2 except for Xucw71, XbarcI01, and Xbarc136, which were described before (Uauy et al., Theor. Appl. Genet. 112, 97, 2005).

¹L = Langdon, D (shaded) = RSL65, S= susceptible, R = resistant.

TABLE 4 Genotypes and phenotypes of 13 RSLs with the closest recombination events flanking Yr36. Race PST-100 was used for inoculations in all experiments, but additional races may have been present in the field experiments. Daily temperature cycles in the greenhouse were 10/35° C. and in the chambers were 10/25° C.

¹‘L’ (white cells): alleles of the susceptible parent LDN, ‘D’ (shaded cells): alleles of the resistant parent RSL65. Because markers are listed in the same order as they are found on the chromosomes, changes in shading represent recombinant chromosome segments in each RSL. 2The 2007 and 2008 field experiments at UCD are summarized by an overall resistant (R) or susceptible (S) score. The greenhouse experiment was performed at Pullman, WA in 2006. Numbers are averages of infection scores of 6-10 plants ± SEM. R and S superscripts indicate resistant or susceptible classification based on the statistical analyses described below. In the 1^(st) chamber experiment lines were simply classified as resistant or susceptible, whereas in the 2^(nd) experiment leaves were scanned and the percentage of leaf area covered with PST pustules was digitally analyzed using the pd program (FIG. S2). These studies confirmed that Yr36 is located between Xucw 129 and Xucw 1 48, and linked to Xucw125, Xucw126, and Xucw130. ³After the ANOVA, each RSL was compared with LDN and RSL65 controls using Dunnett tests. Lines that were not significantly different from LDN and significantly more susceptible than RSL65 (P < 0.01) were classified as susceptible (“S”), whereas lines that were not significantly different from RSL65 but significantly more resistant than LDN (P < 0.01) were classified as resistant (“R”). IT = Infection type. 0-3 (resistant), 4-6 (intermediate), and 7-9 (susceptible).

TABLE 5 Effect of different PST races on infection scores in RSLs with and without Yr36. Infection score¹ Race RSLs with WKS1 RSLs without WKS1 P value PST-17 2.3 ± 0.3  7.0 ± 0.0² <0.0001 PST-37 3.0 ± 0.0 7.0 ± 0.0 <0.0001 PST-45 1.0 ± 0.0 6.5 ± 0.6 <0.0001 PST-100 1.0 ± 0.0 7.8 ± 0.3 <0.0001 PST-113 1.0 ± 0.0 7.0 ± 0.0 <0.0001 PST-116 1.0 ± 0.0 7.0 ± 0.0 <0.0001 PST-127 4.3 ± 0.6 7.0 ± 0.0 <0.0001 PST-130 3.7 ± 0.6 7.0 ± 0.0 <0.0001 ¹Scale of infection type (IT) (5): 0-3 (resistant, none to trace level sporulation), 4-6 (intermediate, light to moderate sporulation), 7-9 (susceptible, abundant sporulation) ²Some race genotype combinations showed no variation among genotypes (SE = 0), resulting in 0 variance and lack of normality.

Infection scores were obtained from three RSLs with the functional WKS1 allele (65, 241, and 402) and three RSLs with the null allele (504, 17-47, and 39-14) plus the susceptible parental line LDN. These RSLs were the critical ones used to map Yr36 within the Xucw129 and Xucw148 interval (Table 3). A total of 3 to 6 plants per race-genotype combination were evaluated. Genotype averages were used as replications and individual plants were used as subsamples for the statistical analysis. Amongst races virulent on LDN, races representing a wide range of virulences (Table 1) were selected. Yr36 resistance to PST races 100, 101 and 111 was shown before (1).

For all races, RSLs with the WKS1 allele showed lower infection scores (P<0.0001) than RSLs without WKS1, indicating that the gene (s) conferring resistance to these eight PST races is located between markers Xucw129 and Xucw148. This conclusion was further supported by ANOVA using different markers for genotype classification (the model included race, genotype, and race*genotype interaction). When WKS1 was used as the classification variable, the F value (F=1,331) was more than 30-fold higher than when flanking markers Xucw129 (F=42) or Xucw148 (F=39) were used as classification variables. These results confirmed that the gene (s) that determines the resistance to these races is located between Xucw129 and Xucw148.

TABLE 6 PCR, primers used for the functional characterization of WKS genes and for germplasm screening. Gene Function Primer name Primer Sequence SIN TILLING WKS1 Kinase domain Till_1_F1 AAGAATAAAATTGGTTTTTAATTTCGGAAAAGGTC 50 Till_1_R1 ATGGAGGTGTTGGCTTTTGTGAGATGTTT 51 WKS1 START domain Till_1_F2 TGCTGGAACTTGGAGCCATATAAAAATGC 52 Till_1_R2 TGAACGGAGGGAGTGTTAACTAGCATAGG 53 WKS2 Kinase domain Till_2_F3 GCCATGAACAACGAACAATCACACGATA 54 Till_2_R3 TAAGTTGTTACTCAGCCCCAGCGCAATAC 55 WKS2 START domain Till_2_F4 TCTGCTCCCAGACCCACCTCATACTTAAA 56 Till_2_R4 GCAAAAGAGAAAAATGTTAAGCAGCGGAAA 57 Transgenics WKS1 Cloning pWKS1 plasmid YR36_S1F1

58 YR36_S1R4

59 WKS1 Transgenic screening YR36_13104F GTGGCCAAAGGGTAGATTAG 60 YR36_13692R CATCATTGTGCACGAGCTAG 61 WKS1 Confirm WKS1.1-6 WKS1_150F ATGGAGCTCCCACGAAACAAAC 62 transcript WKS1.2-6 WKS1_151R GAGACTAGGACACATAACATTAATTG 63 length WKS1.1 WKS1_174R. ACTTTCACCACTTCCTGAAGAC 64 WKS1 Probe for Southern blot YR36_PF ATCGTCTCAGGCCGTGGTA 65 hybridization YR36_PR CCACTTTGCCTTTGCCTTTA 66 Transcription WKS1 Q-PCR all WKS1.1-6 WKS1_Fl AATCAACATCCATTATTGCGAAGA 67 variants in transgenics WKS1_R1 ATACTTCGTCAGGGCCTCCTATG 68 WKS1 Q-PCR WKS1.1 WKS1_F5 CACAAGTACAATACCTTATGAAGATGG 69 WKS1_R5 CCTGAGCCCAGCAATACTGT 70 WKS1 Q-PCR WKS1.2-6 WKS1_F4 CTCCACTGAAAACCCGTAATG 71 WKS1_R4 AACCAAGAGTTTTACCAGCAATACTG 72 WKS2 Q-PCR WKS2_F1 ATCACGAACGTTTGTTTAGTCAAGAA 73 WKS2_R1 GAGGACCATTTGCAATTGATGTT 74 ACTIN Q-PCR Actin_F ACCTTCAGTTGCCCAGCAAT 75 Actin_R CAGAGTCGAGCACAATACCAGTTG 76 Germplasm  screen WKS1 Kinase domain WKS_K_F ATCCATTGCCAAGTCAACCAC 77 WKS2 WKS_K_R TCACTTCCATGAAGGAGGTC 78 WKS1 Inter domain WKS1_I_F CGAAGAAAATCAACATCCATTATT 79 WKS1_I_R GTGTGGCCATCTACCTCCTC 80 WKS2 Inter domain WKS2_I_F GAAAAATCAGAAATATTTTACGTGGA 81 WKS2_I_R AGCTGCAGTCCCACCTAAAA 82 WKS1 START domain WKS_S_F GGCCACACTGCAATACTATACC 83 WKS2 WKS_S_R CACAAATCCTGGCTGTGGAC 84 Kinase WKS1 Construct for GST- kinase GST_EcoRI_F1

85 fusion protein GST_XhoI_R1

86 ¹Sequences highlighted in gray are SbfI and NotI restriction sites for cloning. The underlined bases correspond to the target sequence. ²Sequences highlighted in grey areEcoRI and XhoI restriction sites for cloning

TABLE 7 WKS1 and WKS2 mutants evaluated for PST resistance. Screened Nucleotide Effect on Reaction to Gene region Allele Line ID change¹ amino acid² PSSM SIFT PST WKS1 Kinase wks1a T6-569³ G 163 A V 55 I 11.5 0.00 Susceptible — T6-89 G 508 A D 170 N 10.4 0.46 Resistant wks1b T6-312³ G 595 A G 199 R 19.7 0.00 Susceptible wks1c T6-480-1³ C 632 T T 211 I 12.6 0.01 Susceptible wks1d T6-138³ G 914 A R 305 H 13.6 0.01 Susceptible START wks1e T6-567³ G 4437 A D 477 N 12.3 0.00 Susceptible WKS2 Kinase — T6-960 C 13 T R 5 * —⁴ — Resistant — T6-480-2³ G 72 A W 24 * — — Resistant START — T6-826 G 2221 A W 379 * — — Resistant ¹The first letter indicates the wild-type nucleotide, the number its position from the ATG start codon, and the last letter the mutant nucleotide. ²The first letter indicates the wild-type amino acid, the number its position from the start methionine, and the last letter the mutant amino acid. ³Complete WKS1 or WKS2 coding regions were sequenced. No additional mutations were found. ⁴PSSM and SIFT scores are not reported for mutations that cause premature stop codons.

From the 117 mutations affecting the kinase and START domains, we selected six in WKS1 and three in WKS2. The three mutations in WKS2 resulted in premature stop codons, but no such mutations were available for WKS1. The WKS1 mutations were ranked using the bioinformatics programs SIFT (Sorting Intolerant From Tolerant) (Ng and Henikoff, Nucleic Acids Res. 31, 3812, 2003) and ParseSNP (Project Aligned Related Sequences and Evaluate SNPs) (Taylor and Greene, Nucleic Acids Res. 31, 3808, 2003) which estimate the severity of each missense change. High PSSM (>10) and low SIFT scores (<0.05) predict mutations with severe effects on protein function.

The M₂ line T6-480 was heterozygous for mutations in both WKS1 (C632T) and WKS2 (G72A) in repulsion. Homozygous M₃ progenies containing mutants for one or the other gene were selected and designated T6-480-1 (WKS1) and 16-480-2 (WKS2).

Five of the 6 selected WKS1 mutants were susceptible and were assigned allele names wks1a through wks1e. T6-89 was the only WKS1 mutation tested with a resistant phenotype. This mutation has the lowest PSSM value and a non-significant SIFT score, suggesting that the mutated amino acid may not be essential for resistance.

None of the WKS2 mutations affected PST resistance suggesting that the gene responsible for resistance is WKS1. The C13T and G72A mutations are upstream of the kinase domain and the G2221A mutation is in the inter-domain region.

TABLE 8 Effect of temperature and PST inoculation on WKS1.1 and WKS1.2-6 transcript levels at 3, 9 and 16 days post inoculation (DPI). Numbers in the body of the Table are P values of the two-way ANOVAs. WKS1.1 WKS1.2-6 Source 3* 9* 16 3 9* 16* Temperature (Temp.) <.0001 <.0001 0.016 0.05 <.0001 0.004 Inoculation (Inoc.) 0.15 <.0001 0.0002 0.0003 <.0001 <.0001 Temp.* Inoc. 0.02 0.92 0.24 0.36 0.13 0.79 *Data was transformed to meet assumptions of normally distributed errors and homogeneity of variance.

A 3-way factorial ANOVA showed significant effects of temperature, inoculation and DPI on WKS1.1 (P<0.0001) and WKS1.2-6 (P<0.0001) transcript levels. The three way interaction of these main effects was also significant in both WKS1.1 (P<0.01) and WKS1.2-6 (P<0.05) analyses. Therefore the analysis for each transcript variant was conducted separately for each DPI.

The interactions between temperature and PST inoculation were not-significant for all 2-way ANOVAs except for WKS1.1 at 3 DPI. At this early stage WKS1.1 was significantly up-regulated (P<0.05) in the inoculated samples at low temperature, whereas no significant differences were detected between control and inoculated samples at high temperature (FIG. 4A). At all other time points PST inoculation consistently down-regulated both transcript variants. The effect of temperature was also consistent across DPI. Higher temperatures significantly increased transcript levels of WKS1.1, whereas those from WKS1.2-6 significantly decreased with higher temperature.

An independent experiment including 12 inoculated and 12 control plants at low temperature 3DPI confirmed the increase of WKS1.1 after inoculation (38%) but the values were more variable and therefore the difference was not significant (P=0.10).

TABLE 9 Distribution of WKS1 and WKS2 among different Triticeae species. Presence or absence of WKS1 and WKS2 was assessed by PCR for three different regions of the gene (Table 6) and by sequencing the PCR products (GenBank accessions FJ154103 to FJ154116). WKS1 WKS2 Species Detected Detected Aegilops longissima ¹, T. turgidum ssp. dicoccoides ². Detected Not Dasypyrum villosum ³, Lophopyrum elongatum ⁴, detected Pseudoroegneria gracillima ⁵, Thinopyrum bessarabicum ⁶. Not Detected Ae. comosa ⁷. detected Not Not Ae. bicornis, Ae. crassa, Ae. markgrafii, Ae. detected detected juvenalis, Ae. mutica, Ae. searsii, Ae. sharonensis, Ae. speltoides, Ae. tauschii, Ae. umbellulata, Ae. vavilovii, Agropyron cristatum, Eremopyrum orientale, Heteranthelium piliferum, Psathyrostachys juncea, Pseudoroegneria libanotica, P. spicata, P. strigosa, Secale cereale, Taeniatherum caput-medusae, Triticum aestivum, T. monococcum, T. turgidum ssp. dicoccum, T. turgidum ssp. durum, T. urartu. ¹Present in G509 (J. G. Waines, FJ154103 and FJ154104) and absent in DV1252 (J. Dvorak). ²See Table 10 for intraspecific variation in WKS1 and WKS2 distribution. ³Present in DV1062 (J. Dvorak, FJ154105 and FJ154106) and absent in D-2990 (D. Dewey). ⁴Present in e3 (J. Dvorak, FJ154107 to FJ154109) and absent in e2 (J. Dvorak). ⁵Present in PI 440000 (FJ154110 and FJ154111). ⁶Present in D-3483 (D. Dewey, FJ154112 and FJ154113). Only kinase and inter-domain PCR products were observed in DV013 and DV727 (J. Dvorak). ⁷Present in G1288, G1289, and G5029 (J. G. Waines, FJ154114 to FJ154116) and absent in G659, G601, G5036, and G5307 (J. G. Waines). The LINE retrotransposon insertion detected in RSL65 in WKS2 intron 10 was not detected in WKS2 from Ae. comosa.

Amongst accessions tested in this study; most species with WKS1, WKS2, or both genes showed intraspecific variability for the presence and absence of these genes. Therefore, other accessions of the species listed in the group with no detected WKS gene may still carry one or both WKS genes. Despite this uncertainty, the results above are sufficient to conclude that the duplication that originated WKS1 and WKS2 predated the divergence of the Triticeae species listed above, and that these two genes have been deleted repeatedly in several Triticeae lineages.

TABLE 10 T. turgidum and T. aestivum germplasm used in the allelic diversity study. Wheat No. WKS1/2 Germplasm Number¹/Variety Name T. turgidum ssp. 16 Present PI428015, PI428113, PI487252, PI503315, PI538672, dicoccoides PI538673, PI538678, PI538688, PI538697, PI538699, 5-61, Southern 7-4, 8-12, 9-36, 19-14, 30-22 population² 24 Deleted PI352324, PI428107, PI428111, PI428117, PI428119, PI428123, PI428126, PI428130, PI428135, PI428139, PI428141, PI428143, PI470981, PI470984, PI487264, PI503313, PI503314, PI538681, PI538719, PI560697, PI560872, 1-22, 27-37, 28-50 T. turgidum ssp. 28 Deleted PI428016, PI428028, PI428036, PI428041, PI428047, dicoccoides PI428055, PI428058, PI428061, PI428065, PI428070, Northern PI428072, PI428079, PI428082, PI428087, PI428089, population³ PI428098, PI428145, PI503310, PI538626, PI554580, PI554581, PI554582, PI554583, PI554584, PI560874, 42-8736, 43-8811, 44-8821 T. turgidum ssp. 23 Deleted PI182743, PI254158, PI254180, PI319868, PI319869, dicoccum PI347230, PI352329, PI352347, PI352352, PI352357, Domesticated PI352367, PI355454, PI355496, PI355498, PI470737, emmer PI470738, PI470739, PI606325, PI94626, PI94627, PI94640, CItr17675, CItr17676 T. turgidum ssp. 40 Deleted Aconchi 89, Adamello, Altar 84, Appio, Appulo, Capelli, durum Ciccio, Cirillo, Colorado, Colosseo, Duilio, Durfort, Cultivated durum⁴ Exeldur, Inrat 69, Karel, Karim, Khiar, Kronos, L35, Langdon, Latino, Maier, Messapia, Mexicali 75, Nefer, Neodur, Ofanto, Produra, Rugby, Russello Sg7, San Carlo, Saragolla, Trinakria, Valbelice, Valforte, Valnova, Varano, Vitron, Wb 881, Zenit Triticum aestivum 45 Deleted Bobwhite⁵, Caledonia, Cayuga, RSI5, Express, Pio Bread wheat 26R61, Kanqueen, CO940610, Eltan, Finch, Foster, Grandin*5/ND614, Harry, Heyne, IDO444, IDO556, Jagger, Jaypee, Jupeteco, KS01HW163-4, Louise, McCormick, McNeal, NY18/Clark's Cream 40-1, OR9900553, Penawawa, Pio 25R26, Pioneer 26R46, PI 610750, PI610752, P91193, P92201, Platte, Reeder/Bw- 277, Rio Blanco, Stephens, SS550, TAM 105, Thatcher, UC1110, USG3209, Weebill, Wesley, Zak, 2174. 5 Present⁶ Glupro, Lassik, Farnum, ND683, PI 638740. ¹PI and CItr germplasm correspond to Germplasm Resources Information Network (GRIN) numbers. Other numbers correspond to ‘Location-Genotype’ identification numbers from the University of Haifa wheat germplasm collection (Nevo et al., Evolution of wild emmer and wheat improvement: population genetics, genetic resources, and genome organization of wheat's progenitor, Triticum dicoccoides., (Springer-Verlag, Berlin, 2002), pp. 364). ²Wild emmer from Israel, Lebanon, and Syria (Luo et al., Theor. Appl. Genet. 114, 947, 2007). ³Wild emmer from Iran, Iraq and Turkey. WKS1 was not found in this sub-population. Tetraploid wheat was domesticated from the Northern populations explaining the absence of Yr36 from the domesticated forms. ⁴The country of origin of the cultivated durum varieties is described in (Uauy et al., Science 314, 1298, 2006). ⁵Deletion of WKS1 and WKS2 in hexaploid Bobwhite was confirmed by Southern blot (FIG. S10). ⁶Yr36 has been found only in varieties selected for the closely linked GPC-B1 gene. Lassik and Farnum are new Yr36 stripe rust resistant varieties from California and Washington (USA), respectively. 

1. An isolated nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain.
 2. The isolated nucleic acid molecule of claim 1, wherein said START domain consists of SEQ ID NO: 1, or a variant or a fragment thereof.
 3. The isolated nucleic acid molecule of claim 1, wherein said kinase domain is a Ser/Thr kinase domain.
 4. The isolated nucleic acid molecule of claim 3, wherein said kinase domain is a non-RD kinase domain.
 5. The isolated nucleic acid molecule of claim 4, wherein said kinase domain consists of SEQ ID NO: 2, or a variant or a fragment thereof.
 6. The isolated nucleic acid molecule of claim 1, wherein said START domain consists of SEQ ID NO: 1 and said kinase domain consists of SEQ ID NO:
 2. 7. The isolated nucleic acid molecule of claim 1, which comprises a nucleotide sequence that encodes a polypeptide selected from WKS1.1 (SEQ ID NO: 3), WKS1.2 (SEQ ID NO: 4), WKS1.3 (SEQ ID NO: 5), WKS1.4 (SEQ ID NO: 6), WKS1.5 (SEQ ID NO: 7) and WKS1.6 (SEQ ID NO: 8), or a variant or a fragment of said polypeptide.
 8. The isolated nucleic acid molecule of claim 7, comprising a nucleotide sequence selected from SEQ ID NO: 9 to
 14. 9. The isolated nucleic acid molecule of claim 8, comprising the nucleotide sequence of SEQ ID NO:
 9. 10. The isolated nucleic acid molecule of claim 1, wherein said polypeptide, or a variant or a fragment thereof, confers to a plant broad spectrum resistance to a plant disease.
 11. The isolated nucleic acid molecule of claim 10, wherein said plant disease is a fungal plant disease.
 12. The isolated nucleic acid molecule of claim 10, wherein said plant is a cereal crop plant and said fungal plant disease is caused by a Puccinia fungus.
 13. The isolated nucleic acid molecule of claim 12, wherein the cereal crop plant is wheat or barley and the fungal plant disease is a rust disease caused by Puccinia striiformis.
 14. The isolated nucleic acid molecule of claim 13, wherein said rust disease is stripe rust caused by Puccinia striiformis f. sp. tritici.
 15. An isolated nucleic acid molecule that is complementary to a nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising SEQ ID NO: 1, SEQ ID NO: 2, or both.
 16. An isolated nucleic acid molecule comprising a nucleotide sequence of SEQ ID NO: 15 having promoter function, or a variant or a fragment thereof, wherein said promoter is temperature sensitive.
 17. The isolated nucleic acid molecule of claim 16, wherein said nucleic acid molecule is operably linked to a heterologous transcribable nucleic acid molecule.
 18. The isolated nucleic acid molecule of claim 17, wherein said heterologous transcribable nucleic acid molecule is a molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain.
 19. The isolated nucleic acid molecule of claim 16, wherein said nucleic acid molecule having promoter function is induced at or above a temperature of about 15° C., said temperature being selected from the group of ranges consisting of 15° C.-35° C., 20° C.-35° C., 20° C.-25° C. and 25° C.-35° C.
 20. A vector comprising an isolated nucleic acid molecule according to claim 1, and optionally a nucleotide sequence encoding a heterologous protein, wherein said nucleic acid molecule is operably linked to a promoter that drives expression of the coding sequence of said nucleic acid molecule in a plant cell.
 21. The vector of claim 20, wherein said promoter is a constitutive promoter, a pathogen-induced promoter, or a temperature-sensitive promoter.
 22. The vector of claim 21, wherein said constitutive promoter is a ubiquitin promoter.
 23. The vector of claim 21, wherein said pathogen-induced promoter is a Puccinia induced promoter.
 24. The vector of claim 21, wherein said temperature-sensitive promoter is comprised of an isolated nucleic acid molecule comprising a nucleotide sequence of SEQ ID NO: 15 having promoter function, or a variant or a fragment thereof, wherein said promoter is temperature sensitive.
 25. A host cell that contains a nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain or a vector comprising said nucleic acid molecule, and optionally a nucleotide sequence encoding a heterologous protein, wherein said nucleic acid molecule is operably linked to a promoter that drives expression of the coding sequence of said nucleic acid molecule in a plant cell.
 26. The host cell of claim 25 that is a plant, bacterial, yeast or insect host cell.
 27. The host cell of claim 26 that is a plant cell.
 28. A transgenic plant comprising the host cell of claim
 27. 29. The transgenic plant of claim 28, which is a wheat plant.
 30. A transformed seed comprising the nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain or a vector comprising said nucleic acid molecule, and optionally a nucleotide sequence encoding a heterologous protein, wherein said nucleic acid molecule is operably linked to a promoter that drives expression of the coding sequence of said nucleic acid molecule in a plant cell.
 31. A method for conferring resistance to stripe rust in a cereal crop plant, said method comprising transforming said plant with a nucleic acid molecule comprising a nucleotide sequence which encodes a polypeptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain or a vector comprising said nucleic acid molecule, and optionally a nucleotide sequence encoding a heterologous protein, wherein said nucleic acid molecule is operably linked to a promoter that drives expression of the coding sequence of said nucleic acid molecule in a plant cell.
 32. The method of claim 31, wherein said cereal crop plant is a wheat plant.
 33. A transgenic cereal crop plant having stably incorporated into its genome a nucleic acid molecule comprising a nucleotide sequence which encodes a pal peptide comprising both a steroidogenic acute regulatory protein-related lipid transfer (START) domain and a kinase domain or a vector comprising said nucleic acid molecule, and optionally a nucleotide sequence encoding a heterologous protein, wherein said nucleic acid molecule is operably linked to a promoter that drives expression of the coding sequence of said nucleic acid molecule in a plant cell.
 34. The transgenic cereal crop plant of claim 33, which is a wheat plant.
 35. A transgenic wheat plant having stably incorporated into its genome a nucleic acid molecule comprising a nucleotide sequence selected from SEQ ID NO: 9 to
 14. 36. The transgenic wheat plant according to claim 35, wherein said nucleotide sequence is of SEQ ID NO:
 9. 37. The isolated nucleic acid molecule of claim 17, wherein said nucleic acid molecule having promoter function is induced at or above a temperature of about 15° C., said temperature being selected from the group of ranges consisting of 15° C.-35° C., 20° C.-35° C., 20° C.-25° C. and 25° C.-35° C.
 38. The isolated nucleic acid molecule of claim 18, wherein said nucleic acid molecule having promoter function is induced at or above a temperature of about 15° C., said temperature being selected from the group of ranges consisting of 15° C.-35° C., 20° C.-35° C., 20° C.-25° C. and 25° C.-35° C. 